Preheat the oven to 400 °F (200 °C) and grease a large sheet pan.
In one bowl, whisk together flour, sugar, baking powder, and salt.
In another bowl, whisk milk, eggs, melted butter or oil, and vanilla if using.
Pour the wet ingredients into the dry ingredients and stir until just combined; batter should remain slightly lumpy.
Pour the batter evenly onto the prepared sheet pan.
Sprinkle crumbled sausage evenly over the batter, then top with shredded cheese.
Bake for 15 to 20 minutes, until the pancake is puffed, set, golden on edges, and cheese is melted.
Remove from oven, cut into squares, and serve warm. Drizzle with maple syrup or add sliced green onions if desired.