Preheat the oven to 375 F, and position a rack in the center of your oven. Spray your doughnut pans with non-stick baking spray.

In a bowl, sift together the flour, sugar, cocoa powder, espresso powder, salt and baking soda, then whisk until evenly distributed.

Separately, whisk together the eggs, sour cream, oil and vanilla. Add the wet ingredients to the dry, and stir together with a spatula just until moistened.

Scrape the batter into a piping bag, and snip off the tip. Pipe the batter into the doughnut pans, filling the molds no more than half full.

Bake the doughnuts for about 8 minutes, until risen and the tops spring back when gently touched.

Cool the doughnuts in the pans for 2 minutes, then turn the pans over onto a cooling rack, letting the doughnuts fall out onto the cooling rack.

If you still have batter left, re-fill the pans with the rest of your batter, and bake a second batch of doughnuts.

In a bowl, combine the sugar with the espresso powder, then use your fingers to rub the espresso powder into the sugar, to really infuse it with the coffee flavor.

While the doughnuts are warm, coat them in the espresso sugar.

Serve the doughnuts warm, or at room temperature.

These doughnuts will stay soft and moist for about 3 days, stored in an airtight container at room temperature, but the sugar will soak into the doughnuts and get a little sticky. To serve the leftover doughnuts, save the espresso sugar and freshen the doughnuts up with a new coat of sugar before serving.