Prep: Preheat oven to 350°F (175°C). Generously grease a 9x13-inch baking dish.
Cook Sausage: In a large skillet, cook the sausage over medium-high heat, crumbling it until browned. Crucially, drain all excess grease thoroughly to prevent a soggy casserole.
Mix Batter: In a large bowl, combine the pancake mix, eggs, milk, maple syrup, melted butter, and vanilla extract. Whisk just until combined—a few lumps are okay. Do not overmix.
Assemble: Pour half the batter into the prepared dish. Sprinkle the cooked sausage evenly over the batter, followed by the shredded cheese (if using). Pour the remaining batter over the top.
Chill (Optional): For best results, cover and refrigerate for at least 8 hours or overnight. This allows the batter to soak, creating a richer texture.
Bake: Bake uncovered for 40-50 minutes. The casserole is done when the top is golden brown and a toothpick inserted in the center comes out clean.
Rest: Let the casserole cool on a wire rack for 5-10 minutes before slicing. This helps it set and ensures clean servings.
