Grease a 9 x 13-inch baking pan with butter. Cut bread into cubes and then 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 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.
When ready to bake the casserole, preheat oven to 350° F. Remove casserole from the fridge and sprinkle crumb mixture evenly over the top. 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. Top with powdered sugar and maple syrup.