To prepare an upside down sausage and mushroom pizza recipe, you'll first need to prepare your ingredients. To do this, first preheat your oven to 400?F (204?C) and line a large baking sheet with parchment paper. Then, slice your sausage into 1/4-inch thick slices and place them on the parchment-lined sheet. Sprinkle the sausage with salt and pepper to taste. Bake your pizza for 20 to 25 minutes or until the cheese is melted and the toppings are bubbling. Remove the pizza from the oven and let it sit for 5 to 10 minutes before slicing it into slices.