Prepare equipment and line baking sheets with parchment paper or silicone mats. Sift powdered sugar and almond flour together and set aside.

Preheat oven to 300°F for 60-90 minutes to ensure temperature stability.

Place bowl over pan with barely simmering water. Add granulated sugar and egg white powder, whisk to prevent clumping.

Add egg whites and whisk until sugar completely melts (test by feeling for granules between fingers).

Transfer to stand mixer bowl. Whip on low 30 seconds, then medium 2 minutes, then medium-high until stiff peaks form (13-15 minutes total).

Add sifted dry ingredients and red food coloring (about 1 tablespoon). Fold gently forming J-shape with spatula.

Continue folding until batter is glossy and flows off spatula in 10-15 seconds, able to draw figure 8s.

Transfer to piping bag. Pipe 90 degrees over template centers for 3-5 seconds, pull up with slight twist.

Bang trays against counter, pop air bubbles with toothpick. Rest until completely dry and firm to touch (up to 2 hours due to food coloring).

Bake one tray at a time for 15-20 minutes until macarons have feet and don't feel jiggly when moved.

For royal icing: Mix powdered sugar and meringue powder. Gradually add water, whip until glossy and flowing. Divide into two bowls, color one black and one yellow. Transfer to piping bags.

Decorate shells by piping black belt line across middle, let dry. Add yellow square buckle in center of belt on half the shells.

For buttercream: Heat treat flour at 350°F for 5 minutes, let cool. Beat butter and sugars 4-5 minutes. Add flour, vanilla, almond extract, and milk if needed.

Fill shells with buttercream, sandwich together, and roll sides in shredded coconut.