Grease 9 x 13-inch baking pan. Tear bread into chunks (or cut into cubes) and evenly distribute in the pan. Whisk together eggs, milk, cream, sugar, and vanilla. Pour evenly over bread. Cover tightly and store in the fridge several hours or overnight.
In a separate bowl, mix flour, brown sugar, cinnamon, and salt. Add butter pieces and cut into the dry mixture until mixture resembles fine pebbles. Store in a Ziploc in the fridge.
When you’re ready to bake the casserole, preheat oven to 350 degrees. Remove casserole from oven and sprinkle crumb mixture 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. (I found 45 minutes was just perfect.)