Sift the almond flour and 100g powdered sugar together twice through a fine-mesh sieve into a large bowl.

In a stand mixer, whisk egg whites and cream of tartar on medium speed until soft peaks form, then gradually add granulated sugar.

Increase speed to high and whisk until stiff, glossy peaks form, adding pink gel coloring in the final minute.

Gently fold the dry ingredients into the meringue using the macaronage technique until the batter flows like lava in a continuous ribbon.

Transfer batter to a piping bag with a small round tip and pipe two diagonal teardrops meeting at the bottom to form heart shapes on a silicone mat.

Tap the baking sheet firmly on the counter to release air bubbles and let shells rest for 40 minutes until a dry skin forms.

Bake at 150 degrees Celsius for 15 minutes; allow to cool completely before removing from the mat.

Beat softened butter with 180g powdered sugar, lemon juice, and zest until light and fluffy.

Match cooled shells by size, pipe buttercream onto the flat side of one shell, and sandwich with a second shell.