Place all ingredients for the cheese sauce in a high-speed blender or food processor. Blend on high speed until smooth and creamy, set aside.
Cook the pasta according to the package directions, drain and set aside. Preheat your oven to 375° F and lightly grease a 9 x 13 casserole dish.
Heat a large skillet over medium heat and add the onion, peppers, and mushrooms. Cook for 2-3 minutes until softened, then add the garlic, stir, and cook another 2 minutes.
Push the veggies to one side of the skillet and crumble the sausage to the other side. Cook until fully browned, then remove from heat. Stir in the marinara or pizza sauce and cooked pasta, plus half of the pepperoni.
Transfer the sausage pasta mixture to the casserole dish, then pour the cheese sauce over the top. Arrange the remaining pepperoni over the top, and bake in the preheated oven for 15-20 minutes or until heated through and bubbly. Garnish with fresh herbs and serve hot.
