Sausage-and-Cheese Pancake Breakfast Casserole

unsalted butter, plus more as necessary and for greasing the baking dish

all-purpose flour

baking powder

baking soda

sugar

Kosher salt

buttermilk

large eggs

half-and-half

freshly ground black pepper

pre-cooked breakfast sausage patties, crumbled

sharp white Cheddar cheese, shredded

scallions, sliced

Pure maple syrup, for serving (optional)