In a clean, dry bowl, whip the egg whites and cream of tartar with an electric mixer until soft peaks form. Gradually add the granulated sugar, a tablespoon at a time, while continuing to whip. Keep whipping until you have stiff, glossy peaks and the sugar has fully dissolved. Rub a little between your fingers to check for grains. Stop once you reach this stage.

Add about a third of the sifted almond mixture to the meringue. Fold it in with a spatula (don't whisk) until well incorporated. Add the remaining almond mixture and continue folding until the batter flows like thick lava and falls in ribbons. You should be able to draw a figure 8 in the batter that dissolves back into itself after about 10 seconds. If adding color, fold in a few drops of gel food coloring during this stage.

Spoon the batter into a piping bag fitted with a 1/4-inch round tip. Line two baking trays with parchment paper or silicone mats (use a dab of batter to stick the parchment down). Pipe 1-inch (2.5 cm) circles onto the trays, holding the bag straight down.

Bang the trays firmly on the counter two or three times to release air bubbles. Pop any remaining bubbles with a toothpick.

Let the piped macarons sit at room temperature for about 40 minutes, or until the surface is dry to the touch and no longer sticky. On humid days, this may take longer.

Preheat your oven to 300°F (150°C). Bake one tray at a time for 15-17 minutes. The macarons are done when the tops are set and they don't wobble on their feet when gently nudged. Let them cool completely on the tray before peeling off the parchment.

Match shells by size. Pipe or spoon filling onto the flat side of one shell and sandwich with a matching shell.