In a food processor, combine the almond flour, powdered sugar and dehydrated apple and pulse until everything is reduced to a well-mixed fine crumb. Add 2 egg whites and food coloring (if using), and pulse until it comes together in a mass.

To make the meringue, which will come together quickly, mix together the water and granulated sugar in a small saucepan and have it at the ready on the stove with a candy thermometer.

Fit a stand mixer with a whisking attachment, or have a large bowl and egg beater ready, place 2 egg whites in the bowl, and have the remaining portion of sugar measured and ready to go nearby.

Turn on the burner under the sugar-water mixture to a medium heat. When it reaches 190 degrees, turn the stand mixer on to full speed (the sugar-water mixture will continue to heat and bubble on the stove while you focus on the eggs). Whip the egg whites until they begin to turn foamy and white, then add the pre-measured granulated sugar in a slow stream. Continue whipping until the egg whites form soft peaks. Turn off the mixer when it reaches this stage.

Meanwhile, keep checking the temperature on the bubbling sugar-water mixture. When it reaches 230 degrees, turn off the heat. Turn the mixer with the whipped egg whites back on. Slowly, carefully, pour the hot sugar syrup into the running mixer (it's easiest to aim to have the sugar hit the side of the mixing bowl and run down into the egg whites, so it doesn't get flung around when it hits the beaters). Continue beating until the mixture is somewhat cool to the touch, and the whites are stiff.

When the egg white-syrup mixture reaches this stage, turn off the mixer. Add a scoop of the meringue to the almond-apple mixture, stirring to lighten it. Gently fold the remainder of the meringue into the lightened almond-apple mixture, taking care to use a light touch and a minimum of strokes to avoid deflating the mixture. You're done when the mixture is well combined, and just begins to sheet off your spatula in a ribbon (versus plopping down).

Transfer the batter into a pastry bag (or, if you don't have one, a plastic bag with the corner snipped off). Line cookie sheets with parchment, and pipe the batter out in 1-inch dots (the cookies will spread, but not by a large amount, so you can make the sheets fairly full). Tap the pan on a counter to release any trapped air bubbles. Let sit for 15 to 20 minutes while oven preheats to 325 degrees, allowing the surface of the piped cookies to dry out slightly and appear less glossy. Bake for 14 to 16 minutes, until dried and set but not colored. Allow to cool on the sheets for a half-hour before removing.