Line 3 heavy baking sheets with parchment/baking paper or Silpat mats. Layer the powdered/icing sugar and ground almonds/almond meal in a food processor. Pulse until the mixture looks like fine meal, about 12 pulses. Pass through a sieve and transfer to a small bowl or to a sheet of parchment/baking paper. Set aside.

Place the egg whites and cream of tartar in the bowl of a stand mixer fitted with the whisk attachment. Make sure that the bowl and the whisk are impeccably clean. Starting on medium speed, whip the whites with the cream of tartar until they look like light foam. The whites should not appear liquid. The foam will be light and should not have any structure.

Slowly rain in the granulated sugar in five additions, trying to aim the stream between the whisk and the side of the bowl. Turn the speed up to high. Continue to whip the meringue until it is soft and shiny. It should look like marshmallow creme (marshmallow fluff). Add the vanilla. Whip the egg whites until the mixture begins to dull and the lines of the whisk are visible on the surface of the meringue. Check the peak. It should be firm. Transfer the whites to a medium bowl.

Fold in the ground almond/almond meal mixture in two increments. Paint the mixture halfway up the side of the bowl, using the flat side of a spatula. Scrape the mixture down to the center of the bowl. Repeat two or three times, then check to see if the mixture slides slowly down the side of the bowl. Add drops of gel color and mix them briefly with a toothpick. Put the mixture in a piping bag fitted with your choice of piping tip (round, 1/4 or 1/2 inch in diameter or 6 - 12 mm). If you dont have a macaron mat, draw circles on baking/parchment paper about 2inches/5cm in diameter turn the paper over before placing on the baking sheets. Pipe shells, I like to count numbers in my head and use the same count for each shell so they end up similar in size.

I pipe inside the circles to about 1 3/4 inches/4.5cm but you can go to 1 1/2 inches (3.8cm) the macarons will spread fill the circle while drying.

Slam each sheet hard four to six times on the counter/worktop. Let the unbaked macarons dry until they look dull but not overly dry. Drying time depends on humidity. In a dry climate, the macarons can dry in 15 to 20 minutes; in a humid climate, it can take 35 to 40 minutes.

While the macarons are drying, heat the oven to 300 F (150 C/130C Fan oven/Gas Mark 2). Bake one sheet at a time on the middle rack. Check in 11 minutes. If the tops slide or move (independently of the feet when you gently twist the top), then bake for 2 to 3 more minutes. Check one or two. If they move when gently touched, put them back in the oven for 1 to 2 more minutes until they dont move when touched. Let the macaroons cool for 10 minutes before removing from the pan. The macarons should release without sticking.

Assemble the macarons: find two macarons similar in size and add a good amount of filling to the bottom of one of them. Place the other on top and squeeze gently to take the filling all the way to the edge. Store in the fridge for 24 hours for perfect texture.

A FEW IMPORTANT NOTES BEFORE YOU START

If you want to add solid color instead of the swirls, add GEL FOOD DYE about 1 minute after you finished incorporating all the granulated sugar in the meringue, at the same time that you add the vanilla extract (or other flavoring of your choice). Stop the machine, lift the whisk and add the color right at the bottom of the whisk, this way it goes smoothly into the batter and will not get splashed everywhere.

If you have almond flour that has been laying around for a while, it is a good idea to dry it in a very low oven before using. You can do that the day before. Just add the flour to a baking sheet (over parchment paper) and place in a 250F oven for 20 to 30 minutes. Let it cool completely and use. Humidity is a big enemy of macarons, so if my almond flour has been open for more than a month, I do that just as added precaution.

Hollows. DO NOT worry about them. For the most part they will fill once you add the filling and place in the fridge. Particularly in your first batches, dont worry about perfection. They happen, and they almost always go away through maturation.