Spray a 9x13" baking dish with nonstick cooking spray then spread 3/4 cup of frozen blueberries out in the prepared dish in an even layer.
1 1/2 cups frozen blueberries
Cut all of the pancakes in half and arrange them upright, and overtop of the berries, in rows. Set aside.
18 frozen buttermilk pancakes
Add the eggs, cream, milk, 1/3 cup of sugar, and extract to a large mixing bowl. Whisk them together until well combined then pour the mixture evenly out over the pancakes. Set aside and let the dish rest for 20 minutes.
4 large eggs, 1 cup heavy cream, 1 cup whole milk, 1/3 cup brown sugar, 2 tsp vanilla extract
Add the flour, oats, butter, remaining sugar, and salt to another mixing bowl and whisk together to evenly combine. Spread the streusel topping evenly out overtop of the casserole.
1/4 cup flour, 1/4 cup quick oats, 2 tbsp butter, 2 tbsp brown sugar, 1/8 tsp salt
Top with the remaining blueberries, then cover the dish tightly with foil.
Bake at 350° for 40 minutes. Carefully remove the foil from the dish and bake for another 20 minutes, or until the eggs are set.
Carefully remove the hot dish from the oven, and let it rest for 15 minutes.
Slice, serve, and enjoy!