Buttermilk Marble Cake

Step 1

Preheat the oven to 350 degrees. Grease a 9-inch tube pan with butter and dust with flour.

Step 2

Make the cake: In a medium bowl, sift together flour, baking powder, 1/2 teaspoon baking soda, the salt and 1 2/3 cups sugar.

Step 3

Put the dry ingredients in the bowl of a stand mixer fitted with the paddle attachment. Add the butter and mix on low speed until well blended; do not beat. Combine the buttermilk and vanilla and stir into the flour mixture, until just blended. Add the eggs and mix until just incorporated. Set aside.

Step 4

Melt 1 ounce chocolate in a medium heatproof bowl set over a pot filled with a few inches of simmering water. Remove from the heat and add the remaining 1/4 teaspoon baking soda, 1 tablespoon sugar and 2 tablespoons very hot water. Whisk together until just blended. Fold 1/4 of the batter (about 1 cup) into the chocolate mixture, to create chocolate batter.

Step 5

Pour the batter into the prepared tube pan, alternating the yellow and chocolate batters (two layers of each, beginning with the vanilla batter and ending with the chocolate batter), then run a knife through the batter to marble it. Bake for about 45 to 50 minutes. Start checking the cake after about 35 minutes; the cake should be a little soft in the middle, just barely bouncing back when touched. Remove from oven and let cool 30 minutes. Unmold onto a platter.

Step 6

To make the icing: Melt the 2 ounces chocolate as described above. In a stand mixer fitted with the paddle attachment, combine the cream cheese and sugar and beat until fluffy, about 2 to 3 minutes. Continue beating and add melted chocolate. If the mixture is too stiff, thin with milk, a tablespoon at a time, to bring it to a spreadable consistency. Spread the icing on the top and sides of the cooled cake.