Combine the dry ingredients (flour, sugar, baking powder, baking soda, and salt) in a bowl; mix together.
In a separate bowl, whisk the eggs, and then add in the liquid ingredients (buttermilk, butter, and vanilla), whisking until well combined.
Add the liquid ingredients into the dry ingredients, and stir until combined.
Spray your skillet with cooking spray (or use butter).
Using a soup ladle (or measure 1/4 measuring cup), pour the batter onto the skillet.
Cook for 2-3 minutes on each side; let cool on a plate.
(Pancakes can be made up to 3 days ahead and stored in the fridge.)
To assemble the pancake bake:
Preheat oven to 350 degrees Fahrenheit.
Spray a 13x9-inch baking dish with cooking spray.
Cut the pancakes in half, and being placing the pancakes in the baking dish cut side down, layering them up against each other.
Continue until each pancake is cut and layered into the baking dish.
To make the cinnamon roll filling
Mix together all the ingredients in a small bowl.
With a spreader, layer the filling in between each cut slice of pancake until every pancake has the cinnamon roll filling on it.
To be poured over the bake:
In a large bowl, whisk together the eggs, and add the milk, buttermilk, sugar, and vanilla.
Pour this mixture over the pancakes, making sure each pancake has been coated.
To make the streusel topping:
Mix together the flour, sugar, cinnamon, and salt in a small bowl.
Add into the dry mixture the butter, cutting it into the dry ingredients with a pastry blender or fork until the mixture looks like coarse sand (there will be some pieces larger than others).
Sprinkle the streusel slowly over the pancakes.
Cover the baking dish with sprayed foil and bake for 50 minutes.
Remove the foil and bake for at least another 10 minutes or so, in 10 minute increments, until the top browns and the middle is set (test doneness with a knife - it will come out clear)
Let cool for 15-30 minutes before serving to let it cool before serving.
Serve drizzled with maple syrup and sprinkled with powdered sugar.