Grease a 9 x 13-inch baking pan with butter. Tear bread into chunks (or cut into cubes) and evenly distribute in the pan.
In a medium sized bowl mix together eggs, milk, cream, sugar, and vanilla. Pour evenly over the bread. Cover tightly with plastic wrap and store in the fridge for several hours or overnight.
In a separate bowl, mix flour, brown sugar, cinnamon, and salt. Add nutmeg if desired. Add butter pieces and cut them into the dry mixture until mixture resembles fine pebbles. Store in a Ziploc in the fridge.
In the morning, preheat oven to 350 F. Sprinkle crumb mixture over casserole. Bake for 45 minutes for a softer, more bread pudding texture. Bake 1 hour or more for a firmer, less liquid texture.
Scoop out individual portions.