Fill a pot with about 1-inch of water and bring to a low simmer over medium heat. Whisk together 100g of granulated sugar and 2g of egg white powder (optional) in a large, heat-proof bowl. Pour 100g of egg whites into the bowl and place over the simmering pot. Make sure the water doesn't touch the bottom of the bowl!
Whisk the ingredients together for 2 to 4 minutes, until the sugar has completely melted, and the egg whites have reached 160 F / 71 C. Wipe down the bottom of the bowl with a towel so that it doesn’t drip into the meringue, then pour the egg/sugar mixture into the bowl of a mixer.
Whip the mixture on low speed (2 on a KitchenAid) for 30 seconds. Increase the speed to medium-low (4 on a KitchenAid) for another 30 seconds, then increase it to medium (6 on a KitchenAid). Finish whipping on a medium to medium-high until the meringue achieves stiff peaks (8 on a KitchenAid).
Once the meringue is stiff, sift 105g almond flour, 100g powdered sugar, and 5g freeze-dried fruit powder into the bowl. If you want to use food coloring, add it at this point. Use a circular motion that sweeps around the edge of the bowl and then pull through the bottom of the bowl to make sure everything is getting mixed together. Fold until a thick ribbon of batter runs off the spatula when it is lifted. You should be able to draw a couple figure 8's with the batter running off your spatula when it is the right consistency. If the stream of batter breaks before you're able to this, you may need to stir it a bit more.
Pour the batter into a large piping bag fit with a medium-sized round piping tip and pipe 1 1/2-inch rounds on a large baking sheet lined with a silpat mat, spacing them about 1-inch apart.
Once you finish piping one tray, set the remaining batter aside and bang the pans firmly on the counter or against the palm of your hand a few times to release air bubbles, then pop any remaining air bubbles that come to the surface with a toothpick or scribe.
Use the remaining batter to pipe the second tray of macaron shells and repeat step 6.
As the macarons rest, preheat your oven to 315 F / 158 C. Let the trays rest for about 30 minutes, or until they form a skin and look matte. Once they're ready to bake, you should be able to touch the surface of a macaron shell with your finger without it sticking.
Bake one tray at a time in the middle rack of your oven for 18-21 minutes, or until the shells are fully baked and no longer jiggly. If you notice the shells start to brown, cover them with a foil tent. Leave the oven on (and make the crumble next). Remove the first tray from the oven and bake the second one. Let the macaron shells fully cool on the pan (about 15 minutes), then gently remove them from the silpat mat.