Preheat the oven to 350F. Butter and flour a bundt pan very well.

In the bowl of a stand mixer, beat together the butter and sugar until creamy.

Add in the eggs and vanilla, and beat until fluffy. Stir in the sour cream and mascarpone, and mix until combined.

Add in the flour, cocoa, baking soda, and salt, and beat until creamy and fluffy.

Finally, stir in the chocolate chips.

Pour the batter into the prepared bundt pan, and bake for 60-70 minutes, until a toothpick inserted in the center comes out clean.

Let cake cool slightly in the pan, then invert onto a serving platter. Sprinkle with powdered sugar before serving.