Creamy White Bean Soup with Sage Gremolata

Name: Creamy White Bean Soup with Sage Gremolata
Ingredients: 3 tablespoons olive oil; 1 large yellow onion , chopped; 5 cloves garlic , roughly chopped; 1/4 teaspoon red pepper flakes (optional); 2 cups low-sodium vegetables broth , plus more as needed; 3 ( 14 - ounce ) cans white beans , such as cannellini, including liquid (see recipe note); 1/2 teaspoon kosher salt , plus more to taste; 1/4 teaspoon freshly ground black pepper , plus more to taste; 35 fresh sage leaves (from about 5 sprigs); 1/2 cup loosely packed finely chopped fresh parsley; 1 clove garlic , minced; Finely grated zest of 1 medium lemon (about 1 tablespoon ); 1/8 teaspoon kosher salt