Line two baking sheets with parchment paper. Preheat your oven to 300ºF (or 270ºF for convection).

In a heatproof bowl over simmering water, whisk together granulated sugar and egg white powder until melted. Add egg whites, whipping until stiff peaks form.

Sift almond flour and powdered sugar in a separate bowl. Fold into meringue in three additions, mixing in gel food coloring.

Transfer macaron batter into a piping bag. Pipe small rounds onto prepared sheets, allowing them to rest until a skin forms (approx. 2 hours).

Bake macarons for 15-20 minutes. Allow to cool completely on sheets.

In a clean bowl, mix powdered sugar and meringue powder, adding water to reach glossy consistency. Color with gel food coloring as desired.

Beat together heat-treated flour, unsalted butter, and sugars until creamy. Mix in vanilla and almond extracts, adjusting with milk.

Pipe Sugar Cookie Buttercream onto one macaron shell, sandwich with another shell, and roll edges in desiccated coconut.