Step #1 In a bowl, mix flour, cocoa, baking powder, & salt.
Step #2 In a small bowl, sugar, buttermilk, whisk eggs, & melted butter to mix.
Step #3 Stir into dry ingredients until well mixed.
Step #4 Chill until cold, at least 1 hr or up to 3 hrs.
Step #5 Scrape dough onto a generously floured surface.
Step #6 With floured hands, pat dough out to about 1/2 inch thick.
Step #7 With a 3-inch doughnut cutter, cut out doughnuts.
Step #8 Pat together scraps of dough & cut again.
Step #9 (Alternately, shape dough into ropes about 5 inches long & 1/2 inch thick; join rope ends to form doughnuts.
Step #10 ) Place doughnuts on a well-floured baking sheet.
Step #11 Meanwhile, fill an electric deep-fryer to the fill line or pour about 4 inches of oil into a 5- to 6-quart pan; heat to 375° (see "Fry Right," below).
Step #12 Place one doughnut at a time onto a wide spatula & carefully slide into oil, frying up to three at a time.
Step #13 Cook, until puffy & cooked through, turning once, 3 to 4 mins total (to check timing, cut first one to test).
Step #14 With a slotted spoon, transfer doughnuts to paper towels to drain.
Step #15 Repeat to fry remaining doughnuts.
Step #16 When cool enough to handle, dip the top half of each doughnut in warm mocha glaze & place on a plate.
Step #17 Let stand until glaze is set, about 5 mins.
Step #18 Mocha glaze.
Step #19 In a heatproof bowl, mix 6 oz sliced semisweet chocolate, 2 tsps corn syrup, 1 tbsp butter, 1/2 c whipping cream, & 1 tsp instant espresso powder.
Step #20 Bring a few inches of water to a boil in a pan; remove this from heat.
Step #21 Place bowl over water & let this stand, stirring every once in awhile, until smooth, about 10 mins.