Blueberry Breakfast Muffins

Name: Blueberry Breakfast Muffins
Ingredients: 2 tablespoons unsalted butter, for the muffin tins; 2 cups all-purpose flour; 1 cup blueberries; 1/3 cup granulated sugar; 1 tablespoon baking powder; 1 teaspoon salt; 1 cup buttermilk; 2 eggs, beaten; 2 tablespoons unsalted butter, melted; 1 teaspoon grated lemon zest; 1 teaspoon vanilla extract