Prepare the lemon curd: In a medium heat-proof bowl, whisk together the egg yolks, granulated sugar, lemon juice, lemon zest, and salt until smooth. Place the bowl over a saucepan of simmering water (double boiler), ensuring the water doesn't touch the bottom of the bowl. Whisk continuously until the mixture thickens and coats the back of a spoon (about 170°F/76°C).

Remove the curd from heat and immediately strain through a fine mesh sieve into a clean bowl to remove zest and any cooked egg bits. Whisk in the room temperature butter pieces until fully melted and emulsified. Cover with plastic wrap pressing directly onto the surface of the curd to prevent a skin from forming. Chill in the refrigerator until set.

Prepare the dry ingredients: Weigh the almond flour and powdered sugar. Sift them together through a fine mesh sieve into a large bowl. Discard any large almond pieces that do not pass through. Whisk the sifted mixture to ensure it is fully combined.

Whip the meringue (French Method): In a meticulously clean, grease-free mixer bowl, beat the room-temperature egg whites on medium-low speed until foamy. Add the cream of tartar. Gradually add the granulated sugar, 1 tablespoon at a time, while increasing the speed to medium. Once all sugar is added, beat on medium-high until stiff, glossy peaks form.

Add the gel food coloring to the stiff meringue and whip for 10-15 seconds just to combine. Do not overmix.

Macaronage: Add half of the dry ingredients to the meringue. Fold gently using a silicone spatula, scraping around the bowl and down the middle. Add the remaining dry ingredients and continue folding. As the dry ingredients incorporate, begin pressing the batter gently against the sides of the bowl to deflate some of the air. Stop folding when the batter flows off the spatula in a continuous, thick ribbon like slow-moving lava, allowing you to draw a 'figure 8' without the stream breaking.

Pipe the shells: Transfer the batter to a piping bag fitted with a round tip (about 1/2 inch opening). Hold the bag completely vertical about 1/2 inch above a silicone baking mat-lined baking sheet. Squeeze gently to form 1.5-inch circles, leaving 2 inches of space between them. Release pressure and swiftly pull away in a small circular motion to avoid tails.

Tap the baking sheets firmly on the counter 4-5 times to release trapped air bubbles. Pop any visible surface bubbles with a toothpick.

Rest the shells: Let the piped macarons sit at room temperature until a dry skin forms on the surface. You should be able to gently touch the top of a shell without any batter sticking to your finger. This usually takes 30-60 minutes depending on humidity.

Preheat the oven to 300°F (150°C). Use an oven thermometer to ensure accuracy, as oven displays are often incorrect.

Bake one sheet at a time in the center of the oven for 14-16 minutes. At the halfway point, quickly rotate the pan 180 degrees for even baking. To test for doneness, gently nudge the top of a shell; it should not wiggle significantly from its feet.

Assemble: Once the shells are completely cool, peel them carefully off the mat. Match them up by size. Transfer the chilled lemon curd to a piping bag. Pipe a dollop of lemon curd onto the center of the flat side of one shell, and gently press a matching shell on top until the filling reaches the edges.

Maturation: Place the assembled macarons in an airtight container and refrigerate for 24 hours before eating. This allows the shells to absorb moisture from the filling, creating the signature crisp exterior and chewy, melt-in-your-mouth interior.