Buttermilk-Chocolate Cake

Preheat the oven to 350 degrees F (175 degrees C). Grease a fluted tube pan (such as Bundt®).

Bring 1/2 cup milk to a boil over medium heat. Remove from the heat and add bittersweet chocolate. Let stand for 5 minutes. Stir until smooth, then let cool for 30 minutes.

Stir all-purpose flour, whole wheat flour, baking powder, baking soda, and salt together in a medium bowl.

Beat sugar and margarine in a large bowl with an electric mixer until fluffy. Add eggs, 1 at a time, beating briefly after each addition. Mix in Irish cream liqueur and cooled chocolate mixture. Add flour mixture in 3 batches, alternating with buttermilk, stirring batter briefly after each addition. Pour batter into the prepared pan.

Bake in the preheated oven until top springs back when lightly touched, 50 to 55 minutes. Cool on a wire rack for 10 minutes. Tap the pan a few times and shake it gently to loosen cake. Invert carefully onto a serving plate and let cool completely, about 20 minutes.

Meanwhile, heat milk and oil for ganache in a saucepan over medium heat until boiling. Remove from the heat and add milk chocolate. Let stand for 5 minutes. Stir until smooth, then let cool for 15 minutes. Spread onto cooled cake.