Instructions

  1. Preheat the oven to 350°F. Grease a 10-cup Bundt pan.

  2. In a large mixing bowl using an electric mixer, beat the butter and oil together; add half the cake mix and beat until smooth. 

  3. Reduce the mixer’s speed to low and beat in the eggs one at a time, mixing until each is incorporated before adding the next. 

  4. With the mixer still on low speed, add about 1/3 cup of the milk, then the remaining cake mix, beating until smooth. Mix in another 1/3 cup of the milk.

  5. Transfer 3 cups of the batter to a separate bowl and set aside.

  6. Sift the cocoa with the confectioners’ sugar and add to the remaining batter with the remaining milk. Mix until smooth. 

  7. Spoon alternating scoops of vanilla and chocolate batter into the prepared pan, turning the pan as you go until all the batter from both bowls is used. The pan should be two-thirds full. Pick up the pan and tap it on the counter two or three times to settle the batter fully. 

  8. Bake the cake for 45 to 48 minutes, until a long skewer inserted into it comes out clean; a digital thermometer should register 205°F at the cake's center.  

  9. Remove the cake from the oven and cool in the pan for 10 minutes before turning out onto a rack to cool completely.

  10. Store leftover cake, well wrapped, at room temperature for several days; freeze for longer storage.