Grease a 9x13 pan with butter. Cut bread into bite sized squares and place evenly in pan.
In a bowl mix eggs, eggnog, half and half, brown sugar and vanilla with a whisk until well blended. Pour evenly over the bread.
Cover tightly and store in the fridge for several hours, or overnight.
In a separate bowl mix together the flour, brown sugar, cinnamon, nutmeg, and salt. Cut in the butter with a pastry blender until he mixture looks all crumbly. Place in a ziploc bag and place in the fridge.
When ready to bake, take pan and bag out of fridge. Remove wrap and evenly sprinkle crumb mixture over the top. Bake for 1 hour at 350 degrees (or 45 minutes if you like it more soft and pudding-like.)