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