Tear the French bread into chunks and evenly distribute in the pan.
Whisk together the eggs, milk, heavy whipping cream, granulated sugar, brown sugar, vanilla, and melted butter.
Pour evenly over the bread.
Scatter the blueberries over the top.
To make the topping, mix the flour, brown sugar, ground cinnamon, ground nutmeg and salt in a separate bowl. Stir together using a fork.
With a pastry cutter, gradually work the butter into the flour mixture for about 3 or 4 minutes until it resembles coarse crumbs (about the size of peas) and then scatter over the top of the French toast.
Cover and refrigerate until the morning.
When you’re ready to bake the French toast, preheat the oven to 350°F.
Bake for 45-60 minutes depending on desired texture of the casserole.