diff --git a/shiny/express/_is_express.py b/shiny/express/_is_express.py
index f2f1b643d..c42b5c6db 100644
--- a/shiny/express/_is_express.py
+++ b/shiny/express/_is_express.py
@@ -44,13 +44,30 @@ def is_express_app(app: str, app_dir: str | None) -> bool:
         # Read the file, parse it, and look for any imports of shiny.express.
         with open(app_path) as f:
             content = f.read()
-        tree = ast.parse(content, app_path)
-        detector = DetectShinyExpressVisitor()
-        detector.visit(tree)
+            return is_express_app_content(content)
 
     except Exception:
         return False
 
+
+def is_express_app_content(content: str) -> bool:
+    """
+    Given Python code provided as a string, detect whether it is a Shiny express app.
+
+    Parameters
+    ----------
+    content
+        Python code for the app, provided as a string.
+
+    Returns
+    -------
+    :
+        `True` if it is a Shiny express app, `False` otherwise.
+    """
+    tree = ast.parse(content)
+    detector = DetectShinyExpressVisitor()
+    detector.visit(tree)
+
     return detector.found_shiny_express_import
 
 
diff --git a/shiny/express/_run.py b/shiny/express/_run.py
index cdfc9a9d0..c6e9b56e3 100644
--- a/shiny/express/_run.py
+++ b/shiny/express/_run.py
@@ -1,10 +1,9 @@
 from __future__ import annotations
 
 import ast
-import os
 import sys
 from pathlib import Path
-from typing import cast
+from typing import Mapping, cast
 
 from htmltools import Tag, TagList
 
@@ -82,10 +81,16 @@ def express_server(input: Inputs, output: Outputs, session: Session):
     app_opts = _merge_app_opts(app_opts, mock_session.app_opts)
     app_opts = _normalize_app_opts(app_opts, file.parent)
 
+    # If there's a `ui` option in the app_opts, then use that as the UI instead of the
+    # one that was generated by running the app code.
+    if "ui" in app_opts:
+        app_ui = app_opts["ui"]
+        del app_opts["ui"]
+
     app = App(
         app_ui,
         express_server,
-        **app_opts,  # pyright: ignore[reportArgumentType]
+        **app_opts,  # pyright: ignore[reportArgumentType, reportCallIssue]
     )
 
     return app
@@ -195,14 +200,15 @@ def __getattr__(self, name: str):
 
 class AppOpts(TypedDict):
     static_assets: NotRequired[dict[str, Path]]
+    ui: NotRequired[Path]
     debug: NotRequired[bool]
 
 
 @no_example()
 def app_opts(
-    static_assets: (
-        str | os.PathLike[str] | dict[str, str | Path] | MISSING_TYPE
-    ) = MISSING,
+    *,
+    static_assets: str | Path | Mapping[str, str | Path] | MISSING_TYPE = MISSING,
+    ui: str | Path | MISSING_TYPE = MISSING,
     debug: bool | MISSING_TYPE = MISSING,
 ):
     """
@@ -230,7 +236,7 @@ def app_opts(
         return
 
     if not isinstance(static_assets, MISSING_TYPE):
-        if isinstance(static_assets, (str, os.PathLike)):
+        if isinstance(static_assets, (str, Path)):
             static_assets = {"/": Path(static_assets)}
 
         # Convert string values to Paths. (Need new var name to help type checker.)
@@ -238,6 +244,11 @@ def app_opts(
 
         mock_session.app_opts["static_assets"] = static_assets_paths
 
+    if not isinstance(ui, MISSING_TYPE):
+        if not isinstance(ui, (str, Path)):
+            raise TypeError(f"ui must be a string or Path, not {type(ui).__name__}")
+        mock_session.app_opts["ui"] = Path(ui)
+
     if not isinstance(debug, MISSING_TYPE):
         mock_session.app_opts["debug"] = debug
 
@@ -256,6 +267,9 @@ def _merge_app_opts(app_opts: AppOpts, app_opts_new: AppOpts) -> AppOpts:
     elif "static_assets" in app_opts_new:
         app_opts["static_assets"] = app_opts_new["static_assets"].copy()
 
+    if "ui" in app_opts_new:
+        app_opts["ui"] = app_opts_new["ui"]
+
     if "debug" in app_opts_new:
         app_opts["debug"] = app_opts_new["debug"]
 
@@ -264,8 +278,8 @@ def _merge_app_opts(app_opts: AppOpts, app_opts_new: AppOpts) -> AppOpts:
 
 def _normalize_app_opts(app_opts: AppOpts, parent_dir: Path) -> AppOpts:
     """
-    Normalize the app options, ensuring that all paths in static_assets are absolute.
-    Modifies the original in place.
+    Normalize the app options, ensuring that all paths in `ui` and  `static_assets` are
+    absolute. Modifies the original in place and returns it.
     """
     if "static_assets" in app_opts:
         for mount_point, path in app_opts["static_assets"].items():
@@ -273,4 +287,8 @@ def _normalize_app_opts(app_opts: AppOpts, parent_dir: Path) -> AppOpts:
                 path = parent_dir / path
             app_opts["static_assets"][mount_point] = path
 
+    if "ui" in app_opts:
+        if not app_opts["ui"].is_absolute():
+            app_opts["ui"] = parent_dir / app_opts["ui"]
+
     return app_opts
diff --git a/shiny/quarto.py b/shiny/quarto.py
index 5f0d5efc2..a6ca183c8 100644
--- a/shiny/quarto.py
+++ b/shiny/quarto.py
@@ -32,17 +32,11 @@ def convert_code_cells_to_app_py(json_file: str | Path, app_file: str | Path) ->
     import json
     from textwrap import indent
 
+    from .express._is_express import is_express_app_content
+
     json_file = Path(json_file)
     app_file = Path(app_file)
-
-    if app_file.exists():
-        with open(app_file, "r") as f:
-            first_line = f.readline().strip()
-            if first_line != "# This file generated by Quarto; do not edit by hand.":
-                raise ValueError(
-                    f"Not overwriting app file {app_file}, because it does not appear to be generated by Quarto. "
-                    " If this is incorrect, remove the file and try again."
-                )
+    _check_for_non_autogenerated_file(app_file)
 
     with open(json_file, "r") as f:
         data = cast(QuartoShinyCodeCells, json.load(f))
@@ -63,22 +57,63 @@ def convert_code_cells_to_app_py(json_file: str | Path, app_file: str | Path) ->
             global_code_cell_texts.append(cell["text"] + "\n\n# " + "=" * 72 + "\n\n")
         elif "server" in cell["context"]:
             validate_code_has_no_star_import(cell["text"])
-            session_code_cell_texts.append(
-                indent(cell["text"], "    ") + "\n\n    # " + "=" * 72 + "\n\n"
-            )
+            session_code_cell_texts.append(cell["text"] + "\n\n# " + "=" * 72 + "\n\n")
+
+    global_code_text = "".join(global_code_cell_texts)
+    session_code_text = "".join(session_code_cell_texts)
+
+    is_express = is_express_app_content(global_code_text) or is_express_app_content(
+        session_code_text
+    )
+
+    # If the code in the qmd is for a Shiny Express app, then we need to do something
+    # different from a regular Shiny app.
+    if is_express:
+
+        # In a Shiny Express app, during the UI rendering phase, we don't really need
+        # run any code, other than setting up app options. This is because the UI has
+        # already been generated by Quarto, in an HTML file. So after the initial setup,
+        # we check if there's a current session, and if not, we just return.
+        #
+        # The global (or context:setup) code chunks have already been run by Quarto.
+        # Those chunks do not need to be run during the Shiny Express UI phase (because
+        # they were already run during Quarto's UI phase), but they do need to be run
+        # once per session, so they go inside the block that is run `if
+        # _get_current_session() is not None:`.
+        app_content = f"""# This file generated by Quarto; do not edit by hand.
 
-    app_content = f"""# This file generated by Quarto; do not edit by hand.
+from __future__ import annotations
+
+from pathlib import Path
+from shiny.session import get_current_session as _get_current_session
+from shiny.express import app_opts as _app_opts
+
+_static_assets = ##STATIC_ASSETS_PLACEHOLDER##
+_static_assets = {{"/" + sa: Path(__file__).parent / sa for sa in _static_assets}}
+_app_opts(
+    ui=Path(__file__).parent / "{data["html_file"]}",
+    static_assets=_static_assets
+)
+
+if _get_current_session() is not None:
+{indent(global_code_text, "    ")}
+
+{indent(session_code_text, "    ")}
+
+"""
+    else:
+        app_content = f"""# This file generated by Quarto; do not edit by hand.
 
 from __future__ import annotations
 
 from pathlib import Path
-from shiny import App, Inputs, Outputs, Session, ui
+from shiny import App, Inputs, Outputs, Session
 
-{"".join(global_code_cell_texts)}
+{global_code_text}
 
 
 def server(input: Inputs, output: Outputs, session: Session) -> None:
-{"".join(session_code_cell_texts)}
+{indent(session_code_text, "    ")}
 
     return None
 
@@ -97,6 +132,22 @@ def server(input: Inputs, output: Outputs, session: Session) -> None:
         f.write(app_content)
 
 
+def _check_for_non_autogenerated_file(file: Path) -> None:
+    """
+    Check if a file exists and is _not_ autogenerated by Quarto. If so, raise an error.
+    If the file does not exist, or it exists and is autogenerated by Quarto, just
+    return.
+    """
+    if file.exists():
+        with open(file, "r") as f:
+            first_line = f.readline().strip()
+            if first_line != "# This file generated by Quarto; do not edit by hand.":
+                raise ValueError(
+                    f"Not overwriting app file {file}, because it does not appear to be generated by Quarto. "
+                    " If this is incorrect, remove the file and try again."
+                )
+
+
 # =============================================================================
 # HTML Dependency types
 # =============================================================================