1 3/4 (224 g) cups cake flour

1 1/2 teaspoons baking powder

1/2 teaspoon baking soda

1/2 teaspoon salt

1/4 cup (57 g or 1/2 stick) unsalted butter, room temperature

1 cup (200 g ) granulated sugar

2 large eggs

1/3 cup (75 g) sour cream (or plain, low-fat yogurt)

1/4 cup (60 ml) vegetable oil

2 tablespoons vanilla extract

2/3 (160 ml) cup milk

1 cup (2 sticks) unsalted butter

2 1/2 cups (300 g) powdered sugar, sifted

2 teaspoons vanilla extract

1/8 teaspoon salt

1-2 tablespoons milk

Preheat oven to 350° F. Line a cupcake pan with baking cups.
In a medium bowl, whisk together cake flour, baking powder, baking soda and salt. Set aside.
In a large mixing bowl, cream together the butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Beat in the sour cream, vegetable oil, and vanilla extract.
Gradually add in the flour mixture in three parts, alternating with milk (So it goes flour, milk, flour, milk, flour). Mix until batter is uniform and smooth.
Fill baking cups about 2/3 full and bake for 12-14 minutes, or until a toothpick inserted into the center comes out clean. Remove from the oven, transfer cupcakes to a cooling rack, and allow them to cool to room temperature before frosting.
In a large mixing bowl, whip the butter (with a stand mixer or electric hand mixer) until fluffy, about 5 minutes.
With the mixer on low speed, gradually add in the powdered sugar until completely incorporated.
With the mixer on medium speed, add the vanilla and salt, and beat for a minute, until fluffy. Add milk until desired consistency is reached.
Transfer to a frosting bag with tip and frost away!