Buttermilk Chocolate Cake

Name: Buttermilk Chocolate Cake
Prep time: 25 min
Cook time: 45 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 2 cups all-purpose flour; 1 teaspoon baking powder; 1 teaspoon baking soda; 1/2 teaspoon salt; 2 cups sugar; 1/2 cup unsalted butter; 3 tablespoons cocoa powder; 1/2 cup vegetable oil; 1 cup water; 3 eggs; 1/2 cup buttermilk; 1 teaspoon vanilla extract; 3 tablespoon cocoa powder; 1 (16-ounce) box powdered sugar (3 3/4 cups); 1 teaspoon vanilla; 6 to 8 tablespoons buttermilk