Whisk the rice flour, agar-agar, and sugar together in a saucepan.

Add the water, lemon zest, and lemon juice, then cook over medium heat, stirring constantly, until the mixture comes to a boil and thickens.

Remove from the heat.

Let the lemon cream cool to about 50°C.

Blend in the cold vegan butter until smooth and silky.

Transfer to a container, cover with plastic wrap, then refrigerate for a few hours until set and firm enough to pipe.

Bring the water and sugar to a boil in a small saucepan until the syrup reaches 118-120°C.

Whisk the egg whites in a stand mixer until slightly foamy.

Reduce the speed, then slowly pour in the hot syrup in a steady stream.

Increase the speed and continue whisking for 4-6 minutes.

While the meringue is whipping, begin preparing the macaron batter.

Stop when the Italian meringue is stiff, glossy, and just slightly warm.

Blend the almond flour and powdered sugar in a food processor until as fine as possible, then sift through a fine-mesh sieve.

Mix the almond flour mixture with the egg white using a mixer fitted with the paddle attachment until a paste forms.

Add 1/3 of the meringue to the almond paste, then mix on low speed until fully incorporated.

Fold in the remaining Italian meringue in 2 additions, until the batter reaches the ribbon stage.

Do not overmix, but do not undermix either.

An overmixed batter will spread too quickly when piped, while an undermixed batter will be too thick and barely spread at all.

Aim for the right consistency between the two.

Using a No. 10 piping tip, pipe the batter into discs about 4 cm in diameter on a baking sheet lined with a Silpat or silicone mat.

Tap the baking sheet a few times to flatten the batter, then burst any surface bubbles with a toothpick.

Let the shells dry for 30-60 minutes, depending on the humidity in your kitchen.

Do not bake the shells if they are still damp.

Once the shells are dry enough, bake at 150°C for 16–18 minutes, depending on their size.

Let them cool before peeling them away from the silicone mat or parchment paper.

Match the shells by size, then arrange the pairs on a tray, alternating one shell face-up and the other face-down.

Fill a piping bag with the chilled lemon cream, then pipe a small dollop of filling into the center of one shell.

Place the matching shell on top, then press gently to spread the lemon cream.

Before serving, store the filled macarons in an airtight container lined with parchment paper in the refrigerator overnight, or for at least 24 hours.