Lemon Macarons

Preheat the oven to 140°C (fan-assisted).
Line baking trays with parchment paper.
In a large bowl, sift together the almond flour and icing sugar. Add lemon zest and mix well.
In a separate clean bowl, whisk the egg whites until frothy. Add cream of tartar and continue whisking until soft peaks form.
Gradually add caster sugar while whisking continuously until stiff peaks form and the mixture is glossy.
Gently fold the almond flour mixture into the egg whites until just combined. Be careful not to overmix.
If desired, add a few drops of yellow food colouring and gently fold until evenly distributed.
Transfer the mixture to a piping bag fitted with a round tip.
Pipe small rounds onto the prepared baking trays, leaving space between each macaroon.
Tap the baking trays on the counter to release any air bubbles.
Let the macarons rest at room temperature for about 30 minutes, or until a skin forms on the surface.
Bake in the preheated oven for 15-18 minutes, or until the macarons are set and have formed "feet".
Remove from the oven and let cool completely on the baking trays.
Meanwhile, prepare the cream filling by whisking together the double cream, icing sugar, and lemon zest until thickened.
Once the macarons are completely cooled, pipe or spoon a small amount of cream filling onto the flat side of half of the macarons.
Sandwich together with the remaining macarons to form lemon macaroon sandwiches.