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 until pale and fluffy, approximately 3 minutes.
04 - Incorporate eggs one at a time, beating thoroughly after each addition. Blend in vanilla extract until fully combined.
05 - Gradually add flour mixture and buttermilk to the butter mixture in alternating portions, beginning and ending with the dry ingredients. Mix only until just incorporated to avoid tough texture.
06 - Spread batter evenly into the prepared baking dish, smoothing the top with a spatula.
07 - Bake for 30-35 minutes until a wooden toothpick inserted into the center emerges clean or with just a few moist crumbs.
08 - Allow cake to cool in the pan for 15 minutes before carefully transferring to a wire rack to cool completely.
09 - Whisk together powdered sugar, milk, and vanilla extract until smooth and pourable. Adjust milk quantity to achieve desired consistency.
10 - Drizzle the glaze evenly over the completely cooled cake. Allow glaze to set for 15-20 minutes before slicing and serving.