Baked Caramelized Onion & Mushroom Mozzarella Marinara Pasta

1 Preheat oven to 400°F.
4 In a large skillet, heat olive oil and butter over medium heat. Add sliced onions with a pinch of salt and cook, stirring occasionally, for 20–25 minutes until deeply golden and caramelized. Set aside. 
5 Add mushrooms and cook for 8–10 minutes until browned and softened. Stir in garlic, salt, and pepper, and cook for another minute until fragrant. Set aside. 
2 Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente. Reserve ¼ cup of pasta water, then strain the pasta.
3 Return the strained pasta to the same pot over low heat. Add the jar of Rao’s marinara sauce and the reserved pasta water.
6 Add the caramelized onion and mushroom mixture directly into the pot with the pasta and sauce. Mix until everything is fully combined and coated.
7 Transfer to a greased baking dish. Top with shredded, sliced, and grated mozzarella, and parmesan.
8 Bake for 15–20 minutes, until the cheese is melted, bubbling. Broil for 2-5 minutes until cheese is golden. 
9 Let it sit for 5 minutes, then finish with fresh basil, salt and pepper. Serve and enjoy!