Prepare the Blueberry Filling: In a medium saucepan, heat 3 cups of blueberries, sugar, and lemon juice over medium heat until simmering. Mix 1 tablespoon of cornstarch with water and stir into the blueberries until thickened. Remove from heat.

Make the Pancake Batter: Whisk together 2 cups of flour, 2 tablespoons of baking powder, 1 teaspoon of baking soda, ½ teaspoon of salt, and ¼ cup of sugar. In another bowl, combine 2 eggs, 2 cups of buttermilk, and ½ cup of melted butter. Mix wet into dry until just combined.

Assemble the Casserole: Preheat oven to 375°F and grease a 9x13-inch dish. Pour half the batter into the dish, layer with blueberry filling, then pour remaining batter on top.

Bake the Casserole: Bake for 30-35 minutes until golden brown and a toothpick comes out clean.

Prepare the Glaze (Optional): Whisk 1 cup of powdered sugar, 2-3 tablespoons of buttermilk, and ½ teaspoon of vanilla until smooth. Adjust thickness as needed.

Serve and Enjoy: Allow the casserole to cool for 5-10 minutes, then slice and serve warm with glaze, maple syrup, or whipped cream. Garnish with mint leaves if desired.