In a medium saucepan, combine 3 cups of fresh blueberries, ¼ cup of granulated sugar, and 2 tablespoons of lemon juice. Cook over medium heat, stirring occasionally until the mixture begins to simmer and the sugar dissolves completely, about 5 minutes.

In a small bowl, whisk 1 tablespoon of cornstarch with 1 tablespoon of cold water until smooth. Gradually pour this mixture into the simmering blueberry filling, stirring constantly. Continue cooking for an additional 1-2 minutes, allowing the mixture to thicken significantly.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 4 teaspoons of baking powder, 1 teaspoon of baking soda, ½ teaspoon of salt, and 2 tablespoons of granulated sugar. In a separate bowl, whisk 2 large eggs, 2 cups of buttermilk, 4 tablespoons of melted unsalted butter, and 1 teaspoon of vanilla extract until combined. Pour the wet ingredients into the dry ingredients, gently folding until just combined.

Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish thoroughly with melted butter. Pour half of the pancake batter into the bottom of the dish, using a spatula to spread it evenly across the surface.

Spoon the cooled blueberry filling over the batter, distributing it evenly. Careful with the remaining pancake batter, pour and spread it uniformly over the blueberry filling.

Place the assembled casserole into the preheated oven and bake for 30-35 minutes. A toothpick inserted into the center should come out clean when it’s perfectly done.

While your casserole is baking, whisk together 1 cup of powdered sugar, 2-3 tablespoons of buttermilk, and ½ teaspoon of vanilla extract in a small bowl until smooth. Adjust the consistency as desired.

Once baked, remove the casserole and let it cool for a few minutes before slicing. Drizzle with your optional glaze, if using, and serve warm with maple syrup and whipped cream.