Cut panettone into ½ inch cubes, removing any hard crust. Add to a large bowl.
Mix together eggs, milk, sugar, vanilla, and cinnamon.
Pour egg mixture on top of bread, and very gently toss to coat all pieces. Gently pour into the baking dish and arrange evenly. Cover and refrigerate for 2 hours, or overnight.
To bake:
Remove baking dish from the refrigerator while the oven preheats. Preheat oven to 350˚F.
If adding Streusel Topping, mix all ingredients together (use a pastry cutter for ease), (or prepare the night before) and sprinkle over the top of the dish.
Bake uncovered for 45-60 minutes, or until a knife comes out clean. If the top is getting browned before the dish is baked through, tent loosely with foil for the remainder of cook time.
Remove from the oven and allow to rest for 5-10 minutes before serving. The dish will puff up while baking, and settle after it's been out of the oven for a few minutes.
Notes
Regular sliced bread was used to calculate nutrition.
This recipe can be cut in half and prepared in an 8” square pan, following same directions. Check for doneness after 40 minutes.
Refrigerate cooled, leftover casserole in a covered container for up to 3 days.
Smaller portions can be wrapped and stored in zippered bags in the freezer for up to 1 month. Let them thaw in the refrigerator before reheating.
Reheat portions in the microwave or in the air fryer.