Prepare a macaron template by using a large piping tip or small round cookie cutter of about 1 ½" in size to trace circles about 2 inches apart on one sheet of parchment paper. You will place this under another piece of parchment paper when ready to pipe the macaron shells.

In a medium bowl, sift the powdered sugar and almond flour twice.

Whisk lemon zest into the dry ingredients.

Next, heat the egg whites and granulated sugar over a double boiler until the sugar has dissolved or until the temperature is about 120 degrees F.

Transfer the egg white mixture to a large bowl or a bowl of a stand mixer fitted with a whisk attachment. Whisk until the meringue reaches soft peaks. At this point, you can add the food gel.

Continue whisking the meringue until stiff peaks form. The best way to test if it is ready is by turning the bowl upside down. If the meringue does not fall or move at all, then it is ready.

Start the macaronage by folding in ⅓ of the dry ingredients. Mix carefully with a silicone spatula by scraping aroung the sides of the bowl, then through the middle of the batter. Do this a few times until it is mostly combined.

Add the remainder of the dry ingredients, folding with the same gentle method. Once the dry ingredients are fully incorporated, begin spreading the batter along the sides of the bowl to deflate it slightly. I find that this mixing method ensures that the shells do not bake up hollow. Continue scraping around the sides of the bowl and through the middle. The mixture is ready when you can draw several figure eights without the batter breaking.

Transfer the mixture to a piping bag with a small round piping tip (I used Ateco 802). Place your macaron template under another piece of parchment paper on a baking sheet and pipe perpendicular to fill in each heart. Carefully remove the template and tap the baking sheet on the on counter a few times in order to release any air bubbles. It also helps to bang on the bottom of the baking sheet with your hand.

Let the macarons rest for about 30-40 minutes, or until they are dry and no batter comes away when you touch them.

Toward the end of the resting time, preheat the oven to 300 degrees F.

Bake the macarons for about 12 minutes. Allow to cool completely before removing them from the baking sheet.

In a medium bowl, whisk together the sugar, cornstarch, and salt until no lumps remain.

In a medium saucepan over low-medium heat, melt the butter.

Whisk in the sugar mixture, then the lemon juice and egg yolks until fully combined, about 1 minute.

Use a rubber spatula to constantly stir the mixture for another 2-3 minutes or until large bubbles form in the center. Immediately remove from heat.

Strain the lemon curd into a bowl. Press plastic wrap up against the surface to prevent a skin from forming, and chill for at least 2 hours or overnight.

In a double boiler, heat the egg whites, sugar, and salt, whisking frequently until it reaches 160 degrees F or until the sugar is completely dissolved and the egg whites do not feel grainy.

Transfer the bowl to the stand mixer with a whisk attachment. Whisk on high speed until soft peaks form, then add the vanilla.

Continue mixing until stiff peaks form.

Assemble the macarons immediately.

Transfer the meringue and the curd to piping bags with small round tips.

Pair the macaron shells up and pipe the meringue onto the bottom shell around the edges, then the curd in the middle. Place the paired shell on top, pressing down slightly to ensure they stick together.