01 - Preheat oven to 350°F. Thoroughly grease and flour a 9x13-inch baking dish to prevent sticking.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl until evenly distributed.
03 - Beat softened butter and granulated sugar with an electric mixer on medium-high speed for approximately 3 minutes until pale and fluffy.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla extract until fully incorporated.
05 - Alternately add the flour mixture and buttermilk to the butter mixture, beginning and ending with the flour. Mix only until just combined to avoid overworking the batter.
06 - Spread batter evenly into the prepared pan. Bake for 30-35 minutes until a wooden toothpick inserted into the center emerges clean.
07 - Allow the cake to cool in the pan for 15 minutes, then carefully transfer to a wire rack to cool completely before glazing.
08 - Whisk powdered sugar, milk, and vanilla extract together until smooth and pourable. Adjust consistency with additional milk if necessary.
09 - Drizzle the glaze evenly over the completely cooled cake. Allow the glaze to set for approximately 15 minutes before slicing and serving.