Preheat oven to 400°F. Line a muffin tin with paper liners or lightly grease.
Melt your butter and allow to cool slightly.1/4 cup melted butter In a large bowl, whisk together the flour, sugar, baking powder.1 1/2 cups all-purpose flour, 1/2 cup granulated sugar, 2 teaspoons baking powder Add wet ingredients to the flour mixture. Mix with a large spoon until combined.1 large egg (whisked), 1/2 cup milk, 1/4 cup melted butter, 1/2 teaspoon vanilla extract Gently fold in the mixed berries of choice until distributed throughout batter. 2 cups fresh berries or frozen berries Divide batter evenly among the muffin cups, filling about 2/3 full.
Bake muffins for 20-25 minutes in the preheated oven, or until golden brown and a toothpick comes out clean.
Transfer to a wire rack and allow cooled muffins to rest before serving.