In a medium mixing bowl, whisk together both sugars, cinnamon, salt, graham cracker crumbs and flour. Add melted butter (cooled!) and stir everything together with a fork until coarse crumbs form.
to make the French toast bake:
Preheat oven to 350 degrees F.
Grease a 13" x 9" baking dish.
Arrange bread cubes in the dish.
In a large mixing bowl, whisk together milk, eggs, pumpkin puree, vanilla, pumpkin pie spice and sugar.
Pour pumpkin mixture over bread cubes. Gently toss to coat. If you are preparing this dish the night before, cover the dish at this point with saran wrap and refrigerate overnight. In the morning, let the dish sit on the counter for 15 minutes, to come to room temperature.
Sprinkle with graham cracker crumb topping.
Bake 38 to 42 minutes, until top is crunchy and egg mixture is set.
Dust with powdered sugar, if desired.
Serve with maple syrup, if desired.
Notes
If you don't like maple syrup or simply don't have any on hand, add additional ¼ cup of brown sugar to egg-pumpkin mixture. The bake is not sweet enough without the addition of maple syrup. While I know that most folks like to drizzle maple syrup over their French toast, I want to you to know what to expect and have options.
Do not use freshly baked bread for this recipe. It is better to use stale bread (two day old) or toast the bread cubes in the oven before assembling the dish. To toast the bread: preheat oven to 400 degrees F. Arrange bread cubes on a large baking sheet and toast for 7 to 10 minutes. Cool and use in the dish.
Please note, that the nutrition value can vary depending on what product you use. The information below is an estimate.