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

Sift together the almond flour and powdered sugar in a medium bowl.

Beat the egg whites in a clean bowl, gradually adding granulated sugar, cream of tartar, and salt until stiff peaks form.

Fold the sifted almond flour mixture into the whipped egg whites carefully.

Transfer the macaron batter into a piping bag and pipe circles onto the prepared baking sheets.

Allow the piped macaron shells to rest at room temperature for 20-30 minutes.

Bake the macarons for approximately 15-18 minutes until they lift easily off the parchment.

Prepare the buttercream filling by cooking egg yolks with sugar and milk until thick.

Beat in softened butter and vanilla extract until smooth.

Pair macaron shells by size, pipe buttercream onto one shell, then sandwich with another shell.

Store assembled macarons in an airtight container in the refrigerator for at least 24 hours before serving.