01 - Preheat oven to 350°F. Grease and flour a 9x13-inch baking dish.
02 - In a bowl, whisk together flour, baking powder, baking soda, and salt.
03 - In a large bowl, beat butter and sugar with an electric mixer until light and fluffy, about 3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
05 - Alternately add the flour mixture and buttermilk to the butter mixture, starting and ending with the flour. Mix until just combined.
06 - Spread batter evenly in the prepared pan. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
07 - Cool cake in the pan for 15 minutes, then transfer to a wire rack to cool completely.
08 - For the glaze, whisk powdered sugar, milk, and vanilla until smooth and pourable. Drizzle over the cooled cake. Allow glaze to set before slicing.