Grease a 9-by-13-inch baking pan with butter. Tear bread into chunks (or cut into cubes) and evenly distribute in the pan.

Mix together eggs, milk, cream, sugar, and vanilla in a medium sized bowl. Pour evenly over the bread. Cover tightly and store in the fridge for several hours or overnight.

Mix flour, brown sugar, cinnamon, and salt in a separate bowl. Add nutmeg if desired. Add butter pieces and cut them into the dry mixture until the mixture resembles fine pebbles. Store in a zip-top bag in the fridge.

When you're ready to bake the casserole, preheat oven to 350°. Remove the casserole from the fridge and sprinkle the crumb mixture over the top. (If you're using fruit, sprinkle on before the crumb mixture.) Bake for 45 minutes for a softer, more bread pudding-like texture. Bake 1 hour or more for a firmer, crispier texture.

Scoop out individual portions. Top with butter and drizzle with maple syrup.