In a large pan heat olive oil on medium heat. Add onions and sauté until soft (2-3 minutes). Add sausage, rosemary sprig, and crushed red pepper and cook for 2 minute until sausage is cooked through. Fold in Alfredo sauce and bring to a simmer. Cook ravioli according to packaging instructions. Strain ravioli and gently toss with the sauce, add grated Parmigiano Reggiano (optional).