In a large bowl, combine the butter and sugar. Using a hand mixer, cream until light and fluffy.
1½ cups Crystal Sugar, 1/2 cup Unsalted Butter
Add the Eggs while whisking, one at a time and then the single egg yolk.
4 large Egg, 1 large Eggs Yolks
Gradually add the Vegetable Oil, Vanilla Extract and Buttermilk. Whisk until combined and creamy. If you add the ingredients too fast, the batter might look curdled. This will smoothen out when adding the dry ingredients.