In a large mixing bowl, sift the almond flour and confectioner's sugar. Mix using a whisk and set aside.

In a separate large bowl, beat the egg whites using a mixer. When the egg whites are foamy, add the granulated sugar. Continue mixing over high speed until soft peaks.

Add half of the egg white mixture into the almond flour mixture and gently fold using a rubber spatula. Once the almond flour is well incorporated, add the rest of the almond flour mixture and fold until everything is well combined. The batter should be able to drip and fall off the spatula slowly.

With a piping bag, pipe batter into baking sheet lined with parchment paper. The diameter of each macaron should be about 1.5-2 inches, depending on your preferences. Once all the batter is piped out onto the baking sheet, tap the baking sheet onto the counter top a few times to get rid of the air bubbles. Let the piped batter rest at room temperature for at least 30 minutes, until there is no batter sticking to your finger when touched.

Bake the macarons at 300 degrees Fahrenheit, for about 14-15 minutes, depending on the size of your macarons. Once they are done baking, remove from the oven and from the baking sheet, and let cool on a cooling rack.

To make the coconut buttercream filling, combine the coconut milk, confectioner's sugar, and unsalted butter in a bowl using a mixer until well incorporated and creamy. Using a piping bag, pipe the coconut buttercream onto one macaron cookie, and close with another macaron cookie forming a sandwich. Make sure to use two macaron cookies that are similar in size.