In a food processor, blend almond flour, powdered sugar, and granulated sugar separately until very fine

Sift almond flour and powdered sugar into a bowl and set aside

In a stand mixer, whisk egg whites on low until slightly frothy

Add cream of tartar and salt and continue mixing

Slowly add granulated sugar while the mixer runs

Add yellow food coloring and mix until fully incorporated

Whisk to very stiff peaks (bowl can be inverted without batter moving)

Fold dry ingredients into meringue in three additions until batter flows like lava and can form a continuous figure 8

Transfer batter to a piping bag and pipe onto a silicone baking mat

Tap the tray to release air bubbles and level the batter

Bake at 375°F for 12–14 minutes

Let shells cool completely before removing

Buttercream:Sift powdered sugar

Whip room-temperature butter until fluffy

Add yuzu juice powder, yuzu juice, and heavy cream; whisk until smooth

Adjust with more powdered sugar if too loose or a little yuzu juice/cream if too thick

Pipe buttercream onto shells, sandwich, and refrigerate 1 day for crisp tops and a slightly chewy center