Make classic cake doughnuts from scratch with all the flavors of boozy Irish coffee (whiskey included). Espresso powder in the batter lends a pleasantly bitter note while coffee cream and whiskey make a simple yet bold glaze.
Whisk together the flour, granulated sugar, baking powder, salt and nutmeg in a large bowl until completely combined. Whisk together the buttermilk, sour cream, whole egg, yolk, espresso powder, oil and vanilla in a medium bowl until completely combined. Fold the wet ingredients to the dry ingredients just until a soft and sticky dough comes together (do not overwork).
Line a rimmed baking sheet with parchment paper and liberally dust with flour (about 1/3 cup).
Scrape the dough onto the prepared baking sheet. Dust your hands and the top of the dough with more flour, then gently pat out the dough to 3/4 inch thick.
Working on the baking sheet, punch out as many rounds as you can with a 3-inch cutter. Then use a 1-inch cutter to punch out the center of each round. (Dip the cutters in flour before each cut to avoid sticking.) Gather the dough scraps and gently re-roll without overworking the dough. Repeat cutting until all the dough has been used (you should have 8 doughnuts and 8 doughnut holes).
Set a wire rack inside a rimmed baking sheet and line a second rimmed baking sheet with several layers of paper towels. Fit a large heavy pot with a deep-fry thermometer and pour in vegetable oil to a depth of 3 inches. Heat over medium-high until the thermometer registers 375 degrees F.
Fry the doughnuts in batches until deep golden brown, about 2 minutes per side. Transfer to the wire rack and let cool slightly. Fry the doughnut holes until deep golden brown, about 90 seconds per side. Transfer to the wire rack and let drain for 1 minute. Then transfer to the paper-towel lined baking sheet to cool for 10 minutes before glazing. (This two-step process gets a lot more oil out of the doughnuts than using only one method.) Repeat with the remaining dough, making sure the oil returns to temperature between batches.
Whisk together the confectioners' sugar, coffee cream liqueur and Irish whiskey in a medium bowl until the glaze is smooth and the consistency of honey; add more confectioners' sugar if necessary.
Dip each doughnut into the glaze on one side (we like the craggy side, it has more texture for an appetizing appearance), letting the excess drip back into the bowl, then return it to the wire rack. Toss the doughnut holes in the glaze to coat completely and return to the wire rack. Let the glaze set for 10 minutes before serving.
When measuring flour, we spoon it into a dry measuring cup and level off excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)