Preheat oven to 300°F (150°C) degrees.
Put egg whites into a large bowl and beat with an electric mixer at moderate speed until foamy. While beating, add the salt and cream of tartar. Turn speed to high and gradually add the granulated sugar. Continue to beat until the sugar has dissolved and the mixture is stiff and glossy, usually about 2 1/2 minutes.
Now add a few drops of food coloring and beat to combine. (Keep in mind, the color fades as it bakes, so you might want to make it stronger.)
Put the almond flour and confectioner's sugar into a food processor and pulse a few times to combine, then process for 1 to 2 minutes.
Sift the almond meal and confectioner's sugar through a sieve into a large bowl, pressing down on bigger clumps with the back of a spoon. Discard any almond bits that are too big to pass through the sieve; you may have 1 to 2 tablespoons of coarse almond flour to discard.
Transfer half of the almond/sugar mix into the egg white mixture and fold until just combined. Add the almond extract.
Transfer the remaining almond/sugar mix into the mixture and continue to fold, until batter is smooth and lava-like, and "ribbons" off the spatula, usually 2 to 3 minutes. Try not to over-mix, as the piping will continue to work the mixture.
Transfer the batter to a piping bag fitted with a half inch opening or tip, and pipe onto two trays lined with baking paper or silicone baking sheets. Hold the bag vertically and close to the baking sheet and pipe the mixture out in one ‘dollop’ rather than a circular motion. Keep a good space between each cookie half, as it will flatten out a little.
Once done, firmly drop or tap baking sheets 3 times on the table to bring any bubbles to the surface.
Leave the cookies to sit at room temperature 30-60 minutes, depending on the humidity. This step is vital for the macarons to develop "feet." They are ready to bake when you can gently touch the top of a cookie half and it doesn’t feel sticky to the touch.
Bake one tray at a time in the oven until cookies are shiny and rise 1/8 inch to form a "foot," about 20 minutes. (If cookies are browning too quickly on the bottom, slip another baking sheet underneath.) To check whether they’re done, very lightly touch the top of a macaron – if it’s wobbly or slides around on the feet, give it another minute or two. They’re done when if you lift one of the macarons gently, they should just start to pull away from the paper without sticking.
Take out and place baking sheet on wire rack to cool completely and dry out further. Don’t take the macarons off the baking paper while they’re cooling, or they may stick.
Once cool, remove macarons and sandwich with a thin layer of filling (see below).