Preheat an oven to 325 degrees F (165 degrees C). Grease and flour a 10-inch tube pan. Whisk the flour and baking soda together until blended.

In a large bowl, mash the butter, cream cheese, white sugar and brown sugar with a spoon until the mixture is creamy and thoroughly combined. Beat in 1 egg at a time, mixing it in completely before adding the next one. Stir the vanilla extract with the instant espresso powder in a small bowl, and add it to the butter mixture. Stir in until well combined.

Stir the flour mixture into the butter mixture in 1/2-cup quantities until the flour has been thoroughly incorporated. Stir in the chopped dark chocolate. Spoon the batter into the prepared cake pan.

Bake in the preheated oven until a toothpick inserted into the center of the cake comes out clean, about 1 1/2 hours. Start checking for doneness after about 1 hour and 15 minutes. Cool the cake in the pan for about 10 minutes, then turn out onto a cake dish and allow to finish cooling. Dust with confectioners' sugar.