Pasta with Caramelized Onions, Pecorino Romano, and Black Pepper

Name: Pasta with Caramelized Onions, Pecorino Romano, and Black Pepper
Cook time: 45 min
Total time: 45 min
Cuisine: European, Italian, Mediterranean
Ingredients: 1 pound pasta; Salt and coarsely ground pepper; 1 tablespoon unsalted butter; 2 cups caramelized onions; 1 1/2 ounces shredded Pecorino Romanocheese (3/4 cup), plus extra for serving; 1/4 cup chopped fresh parsley; 1 tablespoon white wine vinegar