smash cake recipe

Ingredients: For the Cake: 1 cup all-purpose flour 1 teaspoon baking powder 1/4 teaspoon baking soda 1/4 teaspoon salt 1/3 cup unsalted butter, softened 1/2 cup granulated sugar 1 large egg 1 teaspoon vanilla extract 1/2 cup buttermilk (or milk mixed with 1/2 teaspoon vinegar or lemon juice)