If your bread is not already dried out, place it onto a sheet pan and bake it at 300 degrees F for 10-15 minutes or until dried out. Alternatively, cover the sheet pan and let the bread dry out overnight at room temperature.
Prepare a 7x4-inch baking dish by brushing with a generous layer of butter.
In a large mixing bowl, whisk together the eggs, half and half, vanilla, cinnamon, nutmeg, salt, and maple syrup. Add the dried-out bread and toss the bread with the custard to fully moisten.
Pour the bread and custard into the prepared cake pan and cover with plastic wrap. Refrigerate for at least 8 hours or up to 18 hours. This allows the bread to absorb the custard fully.
When ready to pressure cook, remove the casserole from the refrigerator and remove the plastic wrap. Cover tightly with foil. Pour in 1 ½ cups of cold tap water into the inner pot and then place in the metal trivet. Place the assembled casserole onto the trivet and seal the instant pot.
Set the cooking time to 35 minutes on high pressure.
Once the cooking time has elapsed, allow the pressure to release naturally or do a quick release of pressure. Remove the french toast casserole from the instant pot and remove the foil.
If desired, broil for 3-4 minutes to crisp and brown up the top of the casserole.
Serve with the vanilla glaze or additional maple syrup.
In a large mixing bowl, whisk together the milk and vanilla extract. Add in 1 cup of sifted powdered sugar and whisk to incorporate, adding more milk or powdered sugar as needed until a thick glaze is formed.
Bread: Use any type of bread you like. It is best to cube the bread into 1 to 2-inch cubes so that your bread is stale or dried out so that it can absorb the custard. Half and Half: In place of half and half, feel free to use heavy cream or milk. Even non-dairy milk works.Storage Instructions: Store any leftover french toast casserole in a sealed container for up to 4 days in the refrigerator or in a freezer-safe bag for up to 3 months in the freezer. Reheat individual servings as desired, defrosting overnight first if needed.Keep it from sticking. For easier clean-up, line your cake pan with parchment paper and then butter the parchment paper.Additions: Feel free to add up to ½ cup of chocolate chips, dried fruit, chopped nuts, or chunks of cream cheese to the french toast casserole for additional flavor.The Glaze. You can skip making the glaze if desired, or prepare it the night before and store it in the refrigerator in an airtight container. Give it a good whisk before drizzling over the french toast.