Preheat the oven to 325°F. Arrange an oven rack in the center of the oven. Line muffin tins with 18 paper cupcake liners. Beat the butter and sugars together, on medium speed, until fluffy crumbs form. Add the eggs, vanilla, and coconut extract, beat again until smooth. Add the milk, beat on low speed to combine. Add the flour, baking powder, and salt. Beat again, just until combined. Stir in the coconut.