Step 1

Preheat oven to 350°F and grease and flour a 9x13-inch pan.

Step 2

In the bowl of a stand mixer or using a large bowl and a hand mixer, combine sugar, flour, cocoa, and baking powder. Whisk until no clumps remain and set aside.

Step 3

In a small saucepan combine butter, coca cola, and oil. Bring to a boil.

Step 4

Pour mixture into the flour mixture and beat on medium speed for about 1 minute until combined.

Step 5

Add eggs, buttermilk, and vanilla extract. Beat until combined, about 1 minute.

Step 6

Spread batter into the prepared pan and bake for 30 minutes or until a toothpick inserted in the center comes out with only a few moist crumbs attached.

Step 7

Make the frosting immediately after removing the cake from the oven.

Step 8

Combine butter, cocoa powder and milk in a saucepan and heat up until just boiling.

Step 9

Remove from heat and add powdered sugar and vanilla extract. Whisk until smooth then spread over warm cake quickly. Let cake cool to room temperature.