Cut each roll into 8 cubes. You can take several rolls at a time, cut them in half then each half into fourths.
Spread bread onto a large rimmed baking sheet and bake for about 30 to 40 minutes, or until dry and crisp. Shake the pan occasionally so the bread will dry evenly.
Prepare crockpot by spraying it liberally with nonstick cooking spray.
In a large bowl, combine eggs, milk, cinnamon, vanilla extract, nutmeg, and whisk until well mixed. Add bread cubes to the crockpot then pour the custard mixture over the bread. Press the bread down into the liquid to submerge.
Sprinkle brown sugar over the casserole then top with sliced butter. Top with chopped nuts, if using. Cook until the casserole is set and golden brown, about 3 and half to 4 hours on low heat.
Serve with maple syrup and fresh fruit.
Notes
Some crockpots (like mine) do run hot especially in the back. You can create a collar by folding three or four pieces of heavy duty foil into 4 inch strips that overlap when placed along the back of the crockpot.If you want to remove the French toast casserole (or any casserole) you will need to create a sling. You will need to fit two long pieces of heavy duty foil placed perpendicular to one another inside the crockpot. Be sure there is some overhang. When ready, use the overhanging foil as handles to lift the casserole out. If you are going to cook the casserole later, cover it with plastic wrap and set in the refrigerator for up to two hours.The longer the casserole sits, the more likely your casserole will turn out mushy instead of moist and hearty. If you need to hold the casserole for longer, then I suggest storing the bread at room temperature and storing the egg mixture in the fridge. Assemble the casserole and cook as directed.We get the best results when using the low temperature setting, but you can cook it on high for a couple of hours. If you have very stale bread, you don't have to pre-bake it.