Prepare Blueberry Filling: In a medium saucepan, combine 3 cups of fresh blueberries, granulated sugar, and lemon juice over medium heat. Stir gently and cook until the mixture simmers and the sugar dissolves, about 3-5 minutes. In a small bowl, mix cornstarch with cold water and stir into the blueberry mixture, cooking for another 2 minutes until thickened. Carefully fold in the remaining blueberries, then set aside to cool slightly.

Make Pancake Batter: In a large mixing bowl, whisk together 2 cups of all-purpose flour, baking powder, baking soda, salt, and sugar until blended. In another bowl, whisk the eggs, buttermilk, melted butter, and vanilla extract until smooth. Pour the wet ingredients into the dry ingredients and mix until just combined; it’s okay if a few lumps remain. This batter will create the fluffy base of your Blueberry Buttermilk Pancake Casserole.

Assemble Casserole: Preheat your oven to 375°F (190°C) and grease a 9x13 inch baking dish with butter or cooking spray. Pour half of the pancake batter into the reserved baking dish, spreading it evenly across the bottom. Next, layer the prepared blueberry filling over the batter, ensuring even coverage. Finally, spoon the remaining batter on top, spreading gently to cover the filling without mixing.

Bake: Place the casserole in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean. The Blueberry Buttermilk Pancake Casserole should puff up nicely and have a custard-like texture. Keep an eye on it toward the end of the baking time to avoid overcooking.

Prepare Glaze (Optional): While the casserole is baking, use a medium bowl to whisk together powdered sugar, buttermilk, and vanilla extract until smooth. Adjust the consistency by adding more buttermilk if necessary; it should be pourable yet slightly thick. This glaze will enhance the flavors of your yummy Blueberry Buttermilk Pancake Casserole when drizzled on top.

Serve: Once baked, remove the casserole from the oven and let it cool slightly for about 5-10 minutes to set. Slice into squares and drizzle with the prepared glaze, if using. Serve warm with maple syrup, whipped cream, and freshly chopped mint leaves for a delightful finish.