Heat the oven to 300°F with a rack in the center, and line two large rimmed baking sheets with parchment paper.

Sift the almond flour, powdered sugar, and cocoa powder together into a bowl.

Beat the egg whites with a mixer until foamy, about 1 minute.

Gradually add the granulated sugar and beat on medium-high until glossy, stiff peaks form, 5-7 minutes.

Fold the dry ingredients into the meringue in three additions, scraping and folding until the batter flows in a thick ribbon and a figure eight settles back into the batter in about 10-15 seconds.

Transfer the batter to a piping bag fitted with a 1/2-inch round tip and pipe 1 1/2-inch rounds about 1 inch apart on the prepared sheets.

Tap each sheet firmly on the counter and pop visible air bubbles with a toothpick.

Let the shells stand at room temperature for 30-60 minutes, until the tops feel dry and are no longer tacky.

Bake one sheet at a time for 15-18 minutes, until the tops are set and do not shift when gently nudged.

Cool completely on the sheet before removing.

Put the chocolate and butter in a heatproof bowl.

Warm the cream in a small saucepan over medium heat until steaming and just bubbling at the edges, 2-3 minutes.

Pour the cream over the chocolate, let stand for 2 minutes, then stir until smooth.

Cool the ganache at room temperature for 30-45 minutes, stirring once halfway through, until thick enough to pipe.

Pipe a ring of ganache onto 24 shells.

Add about 1/2 teaspoon marshmallow creme to the center of each, and top with the remaining shells.

Refrigerate the macarons in an airtight container for 12-24 hours.

Bring to room temperature for about 20 minutes before serving.