Beat egg whites with cream of tartar and salt until soft peaks form. Gradually add granulated sugar until stiff, glossy peaks appear. Fold in gel food coloring if desired.

Sift almond flour and powdered sugar together. Fold into meringue using the macaronage technique until the batter flows like lava.

Pipe 1.5-inch circles onto a parchment-lined tray. Tap tray to release air bubbles. Let rest 30–60 minutes to form a skin.

Preheat oven to 300°F (150°C). Bake for 15–18 minutes until “feet” form. Cool completely.

Cook blackberries with sugar and lemon juice until soft. Strain and stir in butter. Beat softened butter with powdered sugar, then fold in blackberry puree.

Pair shells of similar size. Pipe filling onto one shell and sandwich with the other. Refrigerate 24 hours for best flavor.