Prepare two baking sheets by lining them with parchment paper or silicone mats. Preheat your oven to 315°F (157°C).

In a mixing bowl, whip 4 aged egg whites until soft peaks form. Gradually add 1/4 teaspoon cream of tartar, then slowly add granulated sugar while mixing on high until stiff peaks form.

Sift together 1 cup superfine almond flour, 1 cup powdered sugar, and 1/4 cup cocoa powder. Gently fold the dry mixture into the meringue until it flows like a thick ribbon.

Pipe 1 1/4-inch circles onto the prepared baking sheets, leaving space between each. Let them rest for about 30 minutes until firm and matte.

Bake the macarons for 19-23 minutes, rotating halfway through. They are done when they form a 'foot' and can be lifted gently.

For the filling, beat 1/2 cup unsalted butter until fluffy. Gradually mix in 1 cup marshmallow fluff, 1 teaspoon vanilla extract, and a pinch of salt. Add powdered sugar to taste and adjust consistency with 2 tablespoons heavy cream.

Assemble the cooled macaron shells by pairing them and piping a generous dollop of filling onto one shell, then sandwich with the matching shell.

Mature the assembled macarons in an airtight container in the refrigerator overnight to enhance flavors.