This Is The Easiest Vegetarian Bean Soup Recipe Ever — And It's Anything But Bland

Name: This Is The Easiest Vegetarian Bean Soup Recipe Ever — And It's Anything But Bland
Ingredients: 5 tablespoons extra-virgin olive oil, plus more for drizzling; ½ small yellow onion, finely chopped; Kosher salt and freshly ground black pepper to taste; Pinch of dried red pepper flakes; 2 garlic cloves, minced; 4½ cups cooked cannellini beans, or 3 (15-ounce) cans, rinsed and drained; 2½ to 3 cups vegetable stock, store-bought or homemade; 2 tablespoons sherry vinegar; 4 thick-cut slices crusty bread, such as ciabatta; 4 tablespoons grated Parmesan cheese (optional to vegan-ize)