Prepare the Pancakes: Stir together flour, baking powder, baking soda, salt, and 2 teaspoons sugar in a large bowl. Whisk together buttermilk and 2 eggs in a separate bowl; slowly stir into flour mixture. Gently stir in 1/4 cup melted butter. (Batter will be lumpy.) Let stand 5 minutes.

Heat a nonstick griddle over medium-high. When hot, lightly coat with butter. Drop batter by 1/4 cupfuls onto griddle; cook until tops are covered with bubbles and edges look dry, 3 to 4 minutes. Turn and cook until golden brown, 3 to 4 minutes. Repeat with remaining batter to make about 20 pancakes.

Prepare the Casserole: Cut each pancake in half. Lightly grease an 11- x 7-inch baking dish with cooking spray. Stand pancake halves, cut side down, in 2 rows, starting at 1 short end of prepared baking dish, filling dish completely. (Pancake edges will overlap slightly.)

Whisk together cream, milk, 6 eggs, vanilla, cinnamon, and 1/4 cup sugar in a large bowl. Slowly pour mixture over pancakes. Cover and refrigerate at least 8 hours or overnight.

Preheat oven to 350°F. Uncover casserole; top evenly with blueberries. Bake in preheated oven until center is set, 50 to 55 minutes. Let stand 5 minutes.

Heat maple syrup and butter in a small pan over low heat until heated through and butter is melted. Drizzle 1/4 cup syrup mixture over casserole and serve remaining syrup on the side.