3 ounces 72% dark chocolate (2/3 cup; 85g), finely chopped
3 ounces coffee or black tea (1/3 cup plus 1 tablespoon; 85g), hot
1 ounce Dutch process cocoa powder (shy 1/3 cup; 30g)
4 ounces light brown sugar (1/2 cup; 115g)
5 ounces unsalted butter (10 tablespoons; 140g), about 70°F
1 teaspoon (5ml) vanilla extract
1 teaspoon (4g) baking powder
1/4 teaspoon (1g) Diamond Crystal kosher salt; for table salt, use half as much by volume or use the same weight
1 large egg, straight from the fridge
Roughly 9 ounces Homemade Cool Whip, Cherry Pit Whipped Cream, or your favorite frosting (1 3/4 cups; 255g)
6 1/2 ounces all-purpose flour (1 1/3 cups; 185g)
Preheat oven to 350°F and line 2 aluminum half sheet pans with parchment, trimming as needed so it lies perfectly flat. Whisk hot coffee or tea with chopped chocolate and cocoa in a medium bowl until smooth. Combine butter, brown sugar, baking powder, vanilla, and salt in the bowl of a stand mixer fitted with a paddle attachment and mix on low speed to moisten. Increase to medium and cream until fluffy and light, about 5 minutes, pausing at the halfway point to scrape bowl and beater with a flexible spatula. While still mixing, add egg and continue beating until smooth. Reduce speed to low and add 1/3 of flour, followed by 1/3 of the chocolate paste. Alternate between the two, forming a chocolaty batter. Fold once or twice from the bottom up to ensure no streaks of flour or butter remain. Transfer half of batter to a pastry bag fitted with a 5/8- or 1/2-inch round tip.
Dab a little batter under each corner of parchment, then press firmly to secure it to sheet pans. Pipe about fifteen 2 3/4-inch by 1-inch “buns” onto each sheet pan, refilling the bag when needed. Bake until “buns” are puffy and firm, about 8 minutes. Slide parchment onto the counter and cool until no trace of warmth remains. Use immediately or transfer to an airtight container with a sheet of wax paper between each layer; store at room temperature up to 24 hours.
To Finish: Transfer Homemade Cool Whip, Cherry Pit Whipped Cream, or your favorite whipped frosting to a pastry bag fitted with a 5/8- or 1/2-inch round tip. Flip half the “buns” upside down and pipe about 1 tablespoon of filling down the center of each. Top with remaining “buns” and press gently to secure. Enjoy immediately, or refrigerate in an airtight container up to 6 hours.