Preheat oven to 325 degrees. The key to this recipe is in the preparation – have all ingredients measured and ready before you begin. Separate the eggs whites and keep at room temperature until ready to incorporate.
In a food processor, pulse powdered sugar and almond flour. Sift combined mixture 2 times. Whip the room-temperature egg whites on high with a mixer until foamy and then add cream of tartar. Slowly stream in superfine sugar and whip until stiff and shiny, about 2 minutes on high.
Gently fold in desired food coloring and/or flavor extract, sugar and flour mixture into egg white mixture. Fold the ingredients as little as possible until it is smooth, shiny and slightly runny. If it holds its form, it is under mixed. Scoop into piping bag fitted with a small round tip.
Pipe onto a cookie sheet lined with parchment paper, holding the piping bag in one place while applying pressure. Release pressure when a 1” cookie has been formed and gently swirl the tip out of the mixture without forming a peak. This will allow the cookie to remain smooth on top. Let stand at room temperature 30-40 minutes.
Bake in preheated oven at 325 degrees for 5-10 minutes, until cookies are firm and crisp. Be sure to keep a close eye on the cookies – they should not brown on top. Remove cookies from oven and cool.
For a basic meringue filling, place egg whites and sugar in a heatproof bowl over a pan of simmering water. Whisk until sugar dissolves and mixture reaches 160 degrees on a candy thermometer. Remove from heat, whip on high speed until mixture is cool and stiff peaks form, approximately 6 minutes. Beat in vanilla extract. Use immediately.
Sandwich 2 same-size macaroons with 1 teaspoon meringue, flavored buttercream or other desired filling. Serve immediately, or stack between layers of parchment, wrap well in plastic, and freeze for up to 3 months.