Line two baking sheets with parchment paper, cut to size so that it lies completely flat. Set aside.
With a mesh sieve, sift almond flour and powdered sugar together onto a sheet of parchment paper. Discard any large pieces remaining in the sieve.
In a stand mixer or large bowl & electric mixer, whisk the egg whites on medium speed until it becomes frothy like cappuccino foam.
Add in the granulated sugar, ⅓ at a time, while whisking on medium-high speed until all incorporated.
While the egg whites are at soft peaks, add in the food colouring. Keep whisking until meringue reaches stiff peaks.
Add in half of the sifted almond flour mixture and gently fold with a rubber spatula until just incorporated.
Add the rest of the almond flour mixture and continue folding. Smear the batter up around the sides of the bowl and scrape it back together in a folding motion to deflate some air out of the meringue. Stop folding when you can lift up the batter and drip it off the spatula in a figure 8 motion without the batter breaking.
Transfer batter to a piping bag fitted with a round piping tip. Pipe small 1 inch circles onto the prepared baking sheets by holding the piping bag in the same perpendicular position close to the parchment paper and letting the batter move outwards from the tip. Leave about ½ inch to 1 inch space between each macaron.
Firmly bang the baking sheet on the countertop a few times to bring air bubbles to the surface. Sprinkle a bit of crushed oreo over the shells to create a speckled look.
Leave the baking sheets in a cool, dry area to rest macarons for 30 minutes to 1 hour or until you can brush the surface of a macaron with your finger and it doesn't feel sticky. Preheat oven to 300°F while the macarons are resting.
Bake macarons one tray at a time, in the middle rack for about 15 minutes. Remove macarons from oven when the feet have set and the macarons peel cleanly off the parchment paper. Let cool completely before filling.