Chocolate Zucchini Muffins

Name: Chocolate Zucchini Muffins
Ingredients: 1 cup bittersweet chocolate chips; 1 cup milk chocolate chips; 2 cups all-purpose flour; 1 cup unsweetened cocoa powder; 1 1/2 teaspoons instant espresso powder; 1 teaspoon baking powder; 1 teaspoon baking soda; 1 teaspoon kosher salt; 1 cup granulated sugar; 1/2 cup sour cream; 1/2 cup vegetable oil; 1/2 cup packed light brown sugar; 1 tablespoon vanilla extract; 4 large eggs, beaten; 3 cups coarsely grated zucchini (from about 2 medium zucchini); Flaky sea salt, for serving, optional