Spray a 3-quart baking dish with non-stick spray (or grease with butter).
Cut the bread into cubes and evenly distribute them in the pan. In a large mixing bowl, whisk together the eggs, milk, heavy cream, ½ cup brown sugar, granulated sugar, and vanilla. Pour the mixture evenly over the bread, then sprinkle the cinnamon evenly over the top.
Cover the pan tightly with plastic wrap and chill in the refrigerator for 8 hours, or overnight if possible (for best flavor).
When ready to bake, remove the casserole from the refrigerator and take off the plastic wrap. Preheat the oven to 350 degrees F.
Sprinkle the remaining brown sugar on top of the casserole. Bake for 45-60 minutes, until golden brown and baked through. Serve with syrup and fresh fruit, if desired.
Bread: French bread is best, but any bakery bread will work. I suggest brioche, sourdough or Italian bread. Be sure it is dry and crusty. You can cut it into cubes and let the bread sit on a baking tray for 12 hours to speed up this process if it is fresh bread.Leftovers may be kept in an airtight container in the refrigerator for up to 2 days or frozen.Freeze french toast casserole after it is baked and cooled completely. Wrap securely and freeze for up to 3 months. To defrost, bake casserole uncovered at 350 F for 30 minutes.