Divide the egg whites into two bowls with 55 g in each and let them sit on the countertop for an hour to become room temperature.

Prepare the baking tray with a silicone mat or parchment paper.

Preheat the oven at 150ºC fan oven.

In a food processor add the powdered sugar and almond flour and give it a few quick blitz to minimize any bigger almond pieces. It is important not to process them for too long so the almond flour doesn’t start to release any of its oils.

Take a fine-mesh sieve and sieve the powdered sugar and almond flour together in the bowl, to remove any last bigger almond pieces. There should max be 1 teaspoon left in the sieve. Discard the last big pieces. Use a hand whisk and quickly mix the powder sugar and almond flour, so it's well combined. Add one of the egg whites and gel coloring. Remember to put extra gel color as the color will tone down quite a lot when you add the meringue. With a rubber spatula, fold it together so the almond flour and powder sugar is wet and is incorporated completely with the egg whites and gel color. Place a plastic cling film over the wet dough and set it aside while making the meringue.

Whisk the egg whites in a mixer until stiff peaks.

Meanwhile, in a pot, heat up sugar and water to a boil until it reaches 118ºC. Once it reaches 118ºC, immediately take it off the heat and while the mixer is on the highest speed pour the sugar sirup in a steady stream alongside the bowl. Whisk on medium speed until you meringue creates stiff peaks.

Using a rubber spatula fold in ⅓ of the meringue into the almond/powder sugar mixture to make it the mixture a bit thinner. Be sure to have it all mixed together before adding the remaining meringue. With the rubber spatula, scrape the side of the bowl and then take the spatula through the middle of the mixture.

When the first part of the almond mixture is combined then add the remaining meringue until it is well combined. Continue folding until the batter falls nicely off the spatula in a ribbon. You want to get some of the air out of the meringue, but not all of it so be careful when folding the batter together.

Transfer the macaron batter into a piping bag and fill it up with a round tip nozzle at the end. I like you use a Wilton 1A tip.

On a baking tray with a silicone mat or parchment paper, pipe the macaron shells in equal sizes. Around 2 cm in diameter. You can find templates online to print out and lie underneath to help you out.

Gently tap the baking tray on the work surface. This lets any hidden air bubbles out. Puncture the air bubbles with a tooth pick.

Bake them for 12-14 min.

When they are done, let them cool down completely on a cooling rack.

Take the butter out of the fridge and cut it into cubes 30 min before making the buttercream, to let it come to room temperature.

Sieve the confectioners’ sugar.

Once the 30 min has passed, add it to a mixing bowl of a stand mixer, and mix the butter on high speed for 3 min. Scrape down the sides of the bowl and let it mix for 1 min more.

Add the sieved confectioners’ sugar, lime juice, and vanilla extract and let it mix for 4 min.

Transfer the buttercream to a piping bag fitted with the same round nozzle used to pipe the macarons.

When the macaron shells have completely cooled add your filling, and let them sit in the fridge, in an airtight metal cookie container, overnight.