Preheat your oven to 300°F (150°C) and line two baking sheets with parchment paper.

In a small pot, bring water to a gentle simmer. Combine egg whites and granulated sugar in a heatproof bowl over the pot, whisking constantly for about 1 to 1.5 minutes until the sugar dissolves.

Transfer the bowl to a stand mixer and whip the mixture on high speed for 2 to 3 minutes until stiff peaks form.

Sift together the almond flour, unsweetened cocoa powder, and powdered sugar in a separate bowl. Fold this mix into the whipped meringue.

Transfer the macaron batter into a piping bag fitted with a round tip. Pipe circles onto the baking sheets.

Bake the trays in the preheated oven for 13 minutes, rotating halfway through for even baking.

In a mixing bowl, beat together the softened butter and peanut butter until creamy; incorporate the powdered sugar, vanilla extract, and salt.

To assemble, pipe the peanut butter filling onto half of the cooled macaron shells and place the other halves on top.