Prepare the Pancakes: Stir together flour, sugar, baking powder, baking soda, and salt in a large bowl. Whisk together buttermilk and eggs in a medium bowl; gradually stir buttermilk mixture into flour mixture. Gently stir in butter. (Batter will be lumpy.) Let stand for 5 minutes.

Pour about 1/4 cup batter for each Pancake onto a hot (350°F) buttered griddle.

Cook until tops are covered with bubbles and edges look dry, about 3 minutes. Turn and cook until golden brown, about 3 more minutes. (You should make about 30 Pancakes.)

Prepare the Casserole: Cut each Pancake in half. Lightly grease a 13- x 9-inch baking dish with cooking spray. Arrange halves, cut sides down and overlapping slightly, in 3 rows starting at 1 long end of the prepared baking dish.

Whisk together eggs, cream, milk, granulated sugar, and vanilla in a large bowl. Slowly pour egg mixture over Pancakes; cover with plastic wrap, and refrigerate at least 8 hours or overnight.

Preheat oven to 350°F. Make the Streusel: Combine flour, pecans, brown sugar, cinnamon, and salt in a medium bowl; cut butter into flour mixture with a pastry blender (or use your fingers) until mixture is crumbly.

Uncover Casserole, and sprinkle Streusel mixture over the top. Bake, uncovered, in preheated oven until center is set, 50 to 55 minutes. Let stand 5 minutes before serving. Drizzle each serving with maple syrup.