Stir together the confectioners' sugar and almond flour and sift it through a tammie or very open mesh strainer. In a mixer with a whip attachment, whip the whites until frothy. Add the sugar (and food coloring if using) and whip until stiff. Add 1/3 of the almond mixture and fold part way in. Add another 1/3 and fold partway in. Add final 1/3 and fold in leaving a few specks of egg whites. It will look like deflated marshmallow. Place a pastry bag with a close pin holding it shut in a tall round container folding the edge over the rim of the container to fill it easily. Pipe dots of meringue at each corner to stick down some parchment paper on a sheet pan. Pipe rows of kisses 1-inch each (size of a quarter) one half inch apart. Bake about 17 minutes until very light brown. Pour 1/4 cup water under the parchment paper at both ends of the sheet to steam them loose. Let cool and peel off.
Easy Buttercream: In a mixer with a whip attachment whip the butter very well, scraping the bowl often until it's light and fluffy. Add the confectioners' sugar and mix on low. Drizzle in the flavorings with the hot water. Chill up to a week until ready to use, then bring to room temperature.
Pipe macaroons with buttercream and make little sandwiches. Keep in a covered box chilled.