Preheat and prep: Heat your oven to 350°F (175°C). Generously coat a 6-cavity doughnut pan with nonstick spray. If using silicone pans, place them on a baking sheet for stability.

Mix dry ingredients: In a medium bowl, whisk 1 cup all-purpose flour, 1/2 cup unsweetened cocoa powder, 1/2 cup granulated sugar, 1 teaspoon baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon kosher salt, and 1 teaspoon espresso powder (optional) until no streaks remain.

Combine wet ingredients: In a separate bowl, whisk 1/2 cup buttermilk, 2 large eggs, 1/4 cup neutral oil, and 1 teaspoon vanilla until smooth.

Make the batter: Pour the wet ingredients into the dry. Whisk gently until just combined. If adding mini chocolate chips, fold in 1/4 cup. The batter will be thick but spreadable—avoid overmixing.

Fill the pan: Spoon the batter into a piping bag or a zip-top bag and snip the corner. Pipe the batter into each doughnut well, filling about 3/4 full. Smooth tops with a damp finger if needed.

Bake: Bake 10–12 minutes, until the donuts spring back lightly when touched and a toothpick comes out with a few moist crumbs.

Cool: Let the donuts rest in the pan for 5 minutes. Turn them out onto a wire rack to cool completely before glazing.

Glaze or finish: Whisk 1 cup powdered sugar, 2 tablespoons cocoa powder, 3–4 tablespoons milk, and 1/2 teaspoon vanilla until smooth. Dip cooled donuts, let the glaze drip, then set on the rack to firm. For a quicker finish, dust with powdered sugar or roll warm donuts in cinnamon sugar.