Instructions

1. Preheat the oven to 350°F. Grease and line an 8.5 x 4 x 3 inch loaf pan with parchment paper, leaving a slight overhang on both sides.
2. To make the streusel, put the flour, sugar, cocoa, espresso, and salt in a small bowl. Add in the butter and use your fingers to rub it until pea-size crumbs have formed. It’ll seem a little dry at first but will come together as you continue to work it. Stir in the nibs. Set aside.
3. Next, make the cake. In a small measuring cup, stir together the espresso powder and water until dissolved. Sift the flour, baking powder, baking soda, and salt into a large mixing bowl.
4. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium speed until light and fluffy, 3 to 5 minutes.
5. Pause to scrape down the bottom and side of the bowl. Beat in the eggs, one at a time, then beat in he vanilla. Set the speed to low. Beat in half of the dry ingredients, followed by all of the sour cream, then the remainder of the dry ingredients. Set the speed back to medium and beat until aerated.
6. Transfer a quarter of the batter into a small bowl and add the dissolved espresso and the cocoa. Work the mixture together with a wooden spoon until smooth.
7. Using a generous tablespoon, begin to drop alternating dollops of the batters into the prepared pan in a checkerboard-like manner, until they’re all used up. Use a skewer to swirl them into each other to create a marbled effect, being careful not to overdo it, as too much of a drag could muddy it. Cover with streusel.
8. Bake for 50 to 55 minutes, until golden brown. A skewer inserted into the middle should come out clean. Let the cake cool in the pan for 15 minutes before lifting it out and onto a wire rack to cool further. Dust with confectioners sugar before serving.