Begin by sifting together almond flour, powdered sugar, and espresso powder into a large mixing bowl.

In a stand mixer, beat the egg whites until foamy. Add cream of tartar and then gradually add granulated sugar while whisking until stiff peaks form.

Gently fold half of the dry mixture into the meringue, then add the remaining dry ingredients until it achieves a 'flowing lava' consistency.

Prepare a baking sheet with parchment paper and pipe 1-inch rounds of the macaron batter, allowing it to rest for 30-40 minutes.

Preheat your oven to 300°F (150°C) and bake the macarons for 13-15 minutes until they are firm and have a slight foot.

Let the macarons cool for about 10 minutes on the baking sheet, then transfer them to a wire rack to cool completely.

In a large bowl, cream together unsalted butter, sifted powdered sugar, espresso powder, and vanilla extract until light and fluffy.

Pair up macaron shells of similar size, pipe a dollop of buttercream on one shell and sandwich it with another. Refrigerate for 12-24 hours for best flavor.