In a large mixing bowl, whisk together the flour, Dutch-process cocoa powder, granulated sugar, brown sugar, baking powder, baking soda, fine sea salt, and espresso powder for a full 30 seconds until completely uniform with no streaks or cocoa clumps visible.

In a second large bowl, whisk together the eggs, vegetable oil, room-temperature buttermilk, and vanilla extract until combined and slightly foamy. Pour the hot brewed coffee in a slow steady stream while whisking constantly until the wet mixture is uniform and glossy.

Pour the wet ingredients into the dry ingredients all at once. Using a silicone spatula, fold together with slow wide strokes from the bottom of the bowl upward — 20 to 25 strokes maximum, stopping the moment no dry flour streaks remain. Do not overmix. The batter will be thin, dark, and pourable — this is correct.

Using a large cookie scoop or ¼-cup measure, portion the batter evenly into the 12 lined cups, filling each approximately two-thirds full (approximately 65–70g per cup). Do not overfill.

Bake at 350°F (175°C) on the middle rack for 18 to 20 minutes, until the tops spring back when lightly pressed and a toothpick inserted into the center of a middle cupcake comes out with a few moist crumbs — not wet batter, not completely clean. Rotate the tin 180 degrees at the 12-minute mark.

Remove from the oven and cool in the tin on a wire rack for exactly 5 minutes, then transfer the cupcakes individually to the rack. Cool completely — minimum 45 minutes — before frosting.

Beat the softened unsalted butter with a hand mixer on medium speed for 3 full minutes until pale and fluffy. Add the sifted powdered sugar one cup at a time on low speed, beating to incorporate between each addition. Add the fine sea salt, pure peppermint extract, and 2 tablespoons heavy cream. Beat on medium-high speed for 2 minutes until smooth, bright white, and stiff. Adjust consistency with additional heavy cream one teaspoon at a time. Taste and adjust peppermint extract cautiously in ¼ teaspoon increments if needed.

Place finely chopped bittersweet chocolate in a small heatproof bowl. Heat heavy cream in a small saucepan until small bubbles appear at the edges — just below a simmer. Pour over the chocolate, let sit undisturbed for 90 seconds, then stir slowly from the center outward until completely smooth and glossy. Cool at room temperature for 8 to 10 minutes until slightly thickened but still fluid.

Fit a piping bag with a Wilton 1M open-star tip and fill two-thirds full with peppermint buttercream. Pipe a tall spiral swirl onto each cooled cupcake, starting from the center and spiraling outward and upward in two revolutions, finishing with a sharp upward pull.

Using a spoon or squeeze bottle, drizzle the cooled ganache over each frosted cupcake in a back-and-forth zigzag pattern. Immediately scatter crushed candy cane pieces over the ganache while it is still wet. Allow the ganache to set for 5 minutes before serving.