Preheat oven to 350°F. Line a 12-cup muffin tin with cupcake liners. Whisk flour, baking powder, and salt in a bowl; set aside.
Beat butter, oil, and sugar in the bowl of a stand mixer fitted with the paddle attachment on high speed 2 to 3 minutes or until color turns a pale yellow (use a large bowl and hand mixer or whisk, if you'd like to).
Beat in egg and vanilla.
Alternately beat in dry ingredients and buttermilk (3 additions of dry ingredients, 2 additions of buttermilk), starting and ending with the dry ingredients.
Scrape down the bowl, and beat 30 seconds more on medium speed. Divide batter between muffin cups, filling each about 2/3-full.
Bake 18 to 22 minutes or until the cupcake springs back when you touch the top or a toothpick inserted into the center of a cupcake comes out clean.
Cool completely in pan before transferring to a wire rack to cool completely before frosting.