Line two baking sheets with parchment paper or non-stick silicon mats and set aside. Sift the almond flour and powdered sugar together in a large mixing bowl and set aside. If using regular almond, you may considering grinding it further in a food processor (along with the sugar to keep from making almond butter) for extra smooth macarons.
Place the granulated sugar and water in a saucepan over high heat. Bring to a boil and continue to cook until the mixtures registers 238 degrees on a candy thermometer. Remove from heat and let rest for about 30 seconds.
Meanwhile, whisk the eggs whites with an electric mixer until medium-soft peaks. Do not over-mix the whites. They should be soft but able to hold their shape, not dry and clumpy. If using a stand mixer, begin whisking on high when the sugar mixture hits about 210 degrees. The sugar syrup will heat up rather quickly at this point.
Once the sugar mixture is hot and the eggs are whipped, turn the mixer on high speed and carefully pour in the sugar. Pour in the sugar slowly and try to keep it from hitting the whisk to prevent hot sugar splatters. Continue to mix on high until the outside of the mixer bowl returns to room temperature (about 8 minutes). During the last minute or so, add in the gel food coloring, if desired.
Pre-heat oven to 325 degrees F.
Using a large, rubber spatula, begin folding in the meringue mixture into the almond flour mixture in three batches. Use large, deliberate folds – turning the dry ingredients from the bottom of the bowl up to the top. Continue to fold and smooth out the batter until it falls like thick lava off of the spatula – not too stiff and not too runny. Rotate the bowl as you fold and smear the mixture against the sides of the bowl with spatula to knock out some of the air. Do not over-mix.
Fill a piping bag fitted with a medium round piping tip with the macaron batter. Pipe out uniform rounds of the batter, about 1 ¼ inches in diameter, on the prepared baking sheets. When done, rap the bottoms of the baking sheets a few times against a safe work surface to knock out any air bubbles.
Allow the piped macarons to rest at room temperature for 20 to 30 minutes or until the tops feel dry to the touch and are not sticky. Bake for 9 to 12 minutes. When done, the tops of the macarons should "jiggle" ever so slightly but still feel attached to the base. Cool the macarons on the baking sheet for at least 5 minutes before carefully pealing them off the parchment paper or baking mat.