Velvet Brownie Swirl Cake

Ingredients

• 1 1/2 cups vegetable oil
• 1 1/3 cups buttermilk, room temperature
• 3 eggs, room temperature
• 1 1/2 tsp. white vinegar
• 1 1/2 tsp. vanilla extract
• 3 1/2 cups all purpose flour
• 2 1/4 cups granulated sugar
• 1 tsp. baking soda
• 1 tsp. baking powder
• 1 tsp. salt
• 4 tsp. unsweetened cocoa powder
• 3 tb. unsweetened cocoa powder
• 4 oz. bar chocolate, chopped and melted
• 6-9 tb. heavy cream
• 2 cups powdered sugar
• 1 tb. vanila bean paste (or extract)