Prep the dry mix: Sift together almond flour and powdered sugar into a large bowl. Set aside.

Make the meringue: In a clean mixing bowl, beat the egg whites with cream of tartar until foamy. Slowly add granulated sugar and continue beating until stiff, glossy peaks form. Add lime zest and food coloring if using.

Combine the mixtures: Gently fold the almond flour mixture into the meringue, one-third at a time. Continue folding until the batter flows off the spatula in thick ribbons (“lava-like” consistency).

Pipe the macarons: Transfer batter into a piping bag fitted with a round tip. Pipe 1.5-inch circles onto parchment-lined baking sheets. Tap the trays on the counter to release air bubbles.

Rest the shells: Let macarons sit at room temperature for 30 to 60 minutes until the tops are dry to the touch.

Bake: Bake in a preheated oven at 300°F (150°C) for 15–18 minutes. Allow to cool completely before removing from the tray.

Make the buttercream: Beat softened butter until creamy. Add powdered sugar, lime juice, zest, and a pinch of salt. Mix until light and fluffy.

Assemble: Pipe buttercream onto half of the macaron shells, then sandwich with the remaining shells. Store in the refrigerator for at least 24 hours for best texture.