Summer Squash Frittata with Herbs

Name: Summer Squash Frittata with Herbs
Ingredients: 2 medium zucchini or other summer squash, coarsely grated; 2 tablespoons olive oil, divided; 1 small yellow onion, thinly sliced; 2 garlic cloves, thinly sliced; Kosher salt, freshly ground pepper; 1 tablespoon unsalted butter; 12 large eggs, beaten to blend; ⅓ cup crème fraîche or sour cream; ¼ cup ricotta; 2 tablespoons finely grated Parmesan; 1½ cups (packed) mixed fresh tender herbs, such as basil, chives, parsley, and tarragon; 2 teaspoons finely grated lemon zest; 1 tablespoon fresh lemon juice; Crushed red pepper flakes (optional; for serving)