5 oz (140 grams) bittersweet or semisweet chocolate, chopped
1 tsp brewed coffee (optional)
2 1/4 cups (295 grams) all purpose flour
2 1/2 tsp baking powder
1/4 tsp baking soda
1/2 tsp salt
3/4 cup (170 grams) unsalted butter, room temperature
1 1/4 cups (250 grams) granulated white sugar
3 large eggs, room temperature
1 1/2 tsp pure vanilla extract
1/3 cup (80 ml) sour cream or plain yogurt, room temperature
1/2 cup (120 ml) milk, room temperature
Preheat oven to 350 degrees F (180 degrees C) and place rack in center of oven. Butter, or spray with a non stick spray, a 10 inch (25 cm) bundt or tube pan.
In a heatproof bowl, placed over a saucepan of simmering water, melt the chocolate with the coffee. Remove from heat and set aside to cool to room temperature.
Meanwhile, in a separate bowl, sift or whisk together the flour, baking powder, baking soda, and salt.
In the bowl of your electric mixer (or with a hand mixer), beat the butter until smooth. Gradually add the sugar and continue to beat until the mixture is light and fluffy (about 3-5 minutes). Scrape down the sides of the bowl as needed. Add eggs, one at a time, beating well after each addition. Beat in the vanilla extract and sour cream.
With the mixer on low speed, alternately add the flour mixture and the milk to the batter, in three additions, beginning and ending with the flour. Remove a little more than half of the batter and place into a separate bowl. To the remaining batter stir, or beat, in the melted chocolate. Place the batters into the prepared bundt pan by alternating spoonfuls of vanilla batter with the chocolate batter. Then, with the end of a wooden skewer or knife, gently draw swirls through the batter to marbleize it. Don't over mix.
Bake for about 35 - 40 minutes, or until a toothpick inserted in the center just comes out clean. Remove from oven and place on a wire rack to cool for about 20 minutes before removing the cake from the pan to cool completely. Can dust the top of the cake with cocoa powder or powdered sugar. Serve warm or at room temperature. This cake is best the day it's made, but it will keep for a couple of days at room temperature or it can be frozen.
Serves about 10 people.