Ingredients
Equipment
Method
- Position oven rack in the middle of the oven and preheat to 350°F (175°C), then line a standard 12-cup muffin tin with black paper cupcake liners and set aside.
- In a small heatproof bowl, whisk together the ⅓ cup (35g) Dutch-process cocoa powder and ½ cup (120ml) hot water until fully dissolved and smooth, then set aside to cool for 5 minutes.
- In a large mixing bowl, whisk together the flour, granulated sugar, brown sugar, baking soda, and fine sea salt for 20 full seconds until uniformly combined with no dry streaks.
- In a medium mixing bowl, whisk together the eggs, buttermilk, oil, and vanilla extract for 15 to 20 seconds until smooth, glossy, and fully emulsified with no separation visible.
- Pour the wet ingredients into the dry ingredients and fold with a silicone spatula using slow strokes from the bottom of the bowl upward until mostly combined, then pour in the cooled bloomed cocoa mixture and fold again for approximately 20 strokes until the batter is smooth and nearly black with no dry flour streaks remaining.
- Using a medium cookie scoop or ¼-cup measuring cup, portion the batter evenly into the twelve lined cups to exactly two-thirds full, then bake for 17 to 19 minutes until the tops spring back when lightly pressed and a toothpick inserted in the center comes out with a few moist dark crumbs.
- Leave the cupcakes in the tin on a wire rack for exactly 5 minutes, then lift each cupcake out by its liner and transfer to the wire rack to cool completely to room temperature — approximately 45 minutes to 1 hour — before filling or frosting.
- Make the marshmallow filling: beat the softened butter and marshmallow crème together until smooth, then add the sifted powdered sugar, vanilla extract, and pinch of salt and mix until fully combined and the filling holds a soft peak — refrigerate in the piping bag for 10 minutes if it feels too soft to pipe.
- Core the center of each cooled cupcake to approximately ¾ inch (2cm) wide and 1 inch (2.5cm) deep using an apple corer or small paring knife, then pipe the marshmallow filling into each cavity until level with the cupcake surface and press the top of the removed cake plug back over the filling to seal.
- Make the cocoa whipped cream frosting: combine the cold heavy whipping cream, sifted powdered sugar, sifted Dutch-process cocoa powder, and vanilla extract in a chilled mixing bowl and whip on medium-high speed for 2 to 3 minutes until stiff peaks form — stop immediately when the frosting holds a firm defined peak with just the very tip curling over.
- Transfer the frosting to a large piping bag fitted with a Wilton 1M open star tip and pipe a tall spiral swirl onto each cupcake, starting from the outer edge and working inward and upward, finishing with a pull-up at the center peak.
- Dust the frosted cupcakes with Dutch-process cocoa powder through a fine mesh sieve, drizzle with thin zigzag lines of melted bittersweet chocolate, then immediately press 3 to 4 mini marshmallows into the peak of each cupcake while the drizzle is still slightly tacky.
Notes
- Cocoa powder: must be Dutch-process (alkalized) — natural cocoa changes the color, flavor, and rise of these cupcakes significantly.
- Baking soda: test freshness — drop ½ tsp in hot water + vinegar, should bubble hard within 2 seconds. Replace if not.
- Buttermilk: must be full-fat and room temperature — cold buttermilk can cause the batter to look broken or uneven.
- Marshmallow filling: use jarred marshmallow crème only — melted regular marshmallows have a different texture and will not pipe cleanly.
- Heavy cream: must be refrigerator-cold — warm cream will not whip to stiff peaks and the frosting will collapse.
- Butter for filling: must be fully softened to room temperature — cold butter will not blend smoothly with the marshmallow crème.
- Make ahead: bake, fill, and plug cupcakes up to 2 days ahead — frost on the day of serving for best results.
- Storage: refrigerate frosted cupcakes in a tall hard-sided lidded container for up to 3 days — bring to room temperature 15 to 20 minutes before serving.
- Freeze unbaked: batter does not freeze — freeze cooled unfrosted cupcake bases individually wrapped for up to 2 months.
- Scaling: recipe doubles reliably — use only 1½ tsp baking soda when doubling, not 2 tsp, and make frosting in two separate batches.
- Altitude: reduce baking soda by ¼ tsp, increase flour by 2 tbsp, bake at 365°F (185°C), check at 15 minutes.
- Allergens: contains gluten, dairy, and eggs. Soy may be present in some chocolate chip brands — check the label.
- Tip: apply cocoa dusting before the chocolate drizzle — the order produces the clean two-tone contrast visible in the photos.