1. Sift the almond flour and powdered sugar together into a large bowl to ensure a fine, lump-free texture.

2. In a clean bowl, beat the aged egg whites until foamy. Gradually add the granulated sugar while beating to stiff, glossy peaks. Add lemon zest and gel coloring (if using).

3. Gently fold the dry mixture into the meringue. Mix until the batter flows like lava and can form a ribbon or figure-8 without breaking.

4. Transfer the batter to a piping bag with a round tip and pipe even circles onto silicone or parchment-lined baking sheets. Tap trays to remove air bubbles.

5. Rest the piped shells for 30–60 minutes until a skin forms. Bake at 300°F (150°C) for 14–16 minutes. Cool fully before removing.

6. For the filling, beat butter until creamy, add powdered sugar gradually, then lemon juice. Add cream as needed for desired consistency.

7. Pipe buttercream onto half the shells and sandwich with remaining shells. Twist gently to secure. Refrigerate overnight for best results.