Combine the egg whites with the powdered egg whites by stirring in the powdered egg whites in a slow cascading motion with a whisk.
Grind the superfine sugar in a coffee grinder until very fine unless using fondant sugar, in which case you only need to sift it to remove any lumps.
Combine the almond flour with the confectioners’ sugar in a bowl and then mix in a Robot Coupe for 30 seconds; pass through a drum sieve.
In an electric mixer fitted with the whip attachment, whip the egg whites on high speed. When they have reached medium peaks, sprinkle in the sugar, and then whip to stiff peaks. Add a few drops of food coloring if needed at this point. Whip for a few more seconds to fully incorporate the color. The amount of color depends on the type of coloring you use. Natural food coloring is expensive and requires a larger quantity to properly color a base than non-natural colors and they tend to fade with time. Always use liquid soluble colors, not fat-based colors. You may use powdered color as well, just make sure it is liquid soluble and not fat soluble). For the colors used in these macaron recipes resources.
Fold the meringue into the dry ingredients until smooth using a rubber spatula. Do not overmix (it will become very loose). It should puddle a little bit just after you stop stirring. You are not making a sponge cake here, so there will be some deflation in the meringue, but this is expected.
Pour into a piping bag fitted with a #6 plain tip.
Pipe onto a sheet pan lined with a thin, nonstick baking mat (preferably not the rubber mats, since these are too thick; see Resources). Using a perforated mat results in a more efficient heat transfer to the bottom of the macaron, which gives the cookie higher volume. The diameter of the macaron should be about 3.18cm/1.25in. Space them out leaving at least a 2.50-cm/1-in space between them. Let them air-dry for 30 to 40 minutes. Always check by touching the dome of the cookie to feel for a dry surface. Your finger should not leave a dent.
Meanwhile, preheat a convection oven to 150°C/300°F and set to fan speed 3. Bake for 2 minutes, then turn the fan speed down to 1 and bake for 2 more minutes. Turn off the oven and leave the macarons in the oven for 12 to 14 minutes more, or 8 to 10 minutes for small macarons. They are ready when they can be lifted up from the mat without sticking.
Cool at room temperature.
Fill with the appropriate filling. The filling should be placed in a piping bag with a small #2 plain tip. The average thickness of the filling should be about 3mm/.1in but can vary depending on the filling. Too little filling is not recommended; there should be enough in there to be able to tell what flavor it is, but there shouldn’t be too much either. The consistency of the filling is important as well. It shouldn’t be too wet, or it will make the cookie soggy and spill out of the cookie. Ideally, it should hold its shape once it is piped. This is where using a little buttercream can help to tighten up the filling, but remember to use it in moderation.
Place the cookies in a single layer on a sheet pan and cover with plastic wrap. It is crucial not to serve the cookies as soon as they are assembled, since they will need about 24 hours to get acquainted. This means that the filling will soften the base of the cookie it is in contact with and meld both the cookies to it. Some chefs recommend more than 24 hours, but this amount of time is just enough.
Reserve frozen for up to 3 months or refrigerate for up to 7 days, well wrapped in an airtight container.
They can be served straight from the refrigerator or left out to temper for 1 hour before serving. I enjoy them either way. They are even pleasant to eat frozen.