Yes, you can freeze French Toast Casserole after baking. Store leftovers in an airtight container in the freezer for up to 3 months. Allow the french toast casserole to thaw overnight in the fridge. Remove plastic wrap, but cover with foil and then reheat at 350 degrees for 20 minutes or until warmed through. Individual portions can be warmed up in the microwave. Overall, this is easy to do.