Preheat oven to 350 degrees and spray a 9x13 baking pan with pam baking spray
Using a standing mixer, beat butter and sugar until creamy
Beat in eggs one at a time until creamy and combined
Using a medium bowl, whisk together the flour, baking powder, and salt
Using a liquid measuring cup, measure out buttermilk
With the mixer on low, begin adding the dry ingredients to the batter, and alternate pouring in the buttermilk gradually
When all ingredients have been mixed, add the vanilla and mix until completely combined
Pour batter into the baking pan and evenly smooth with a spatula.
Bake for 26-28 minutes or until a toothpick inserted into the cake comes out clean