Preheat oven to 325℉. Grease the mini bundt pan. Set aside.
In a large bowl, whisk together the flour, baking powder, baking soda and salt. Set aside.
In the bowl of a stand mixer, beat the butter and sugar together until light and creamy, about 2 minutes. Add the eggs, one at a time, beating well after each addition. Mix in the vanilla.
With the mixer on the lowest speed, add half the flour mixture and mix just until combined. Then, add the milk in a steady stream. Finish with the remaining flour mixture and mix just until combined.
Transfer about half the batter to a separate bowl. Stir in the cocoa powder and milk.
Use a spoon to transfer some of the vanilla batter to the prepared mini bundt pan. Fill each cup about one-third of the way. Repeat with the chocolate batter. Finish with one or two dollops of vanilla batter. Use a skewer or toothpick to swirl the two together slightly. Each cup should be about ¾ full. (see notes)
Bake the cakes at 325ºF for 20 to 25 minutes or until a toothpick inserted in the center comes out with little to no crumbs. Cool in the pan for about 10 minutes, then invert the cakes onto a wire rack to cool completely.
For the icing, whisk together the confectioners’ sugar, vanilla and milk. Spoon over the tops of the cooled cakes and serve.
Notes
Tip: When filling the cups, try to put the vanilla batter on one side, then the chocolate on the other. It will give the tops a more marbled appearance when removed from the pan. It doesn’t have to be perfect.Store cakes in an airtight container at room temperature for up to 3 days.Grease the mini bundt pan with my magic cake pan release to guaranteed no breakage when releasing the cakes from the pan.