For the macarons:
In the food processor, mix the almond powder and icing sugar together until it's reduced into a very fine powder, for about 2 minutes. Add 2 egg whites and process until smooth.
Cook's Note: the texture will be similar to almond paste.
Add the food coloring and continue processing until the color is all blended in. You can add a few more drops just until you get the color you want. Transfer the mixture to a large bowl and put aside.
In a stockpot, bring the water and sugar to a boil and cook for about 15 minutes, until reduced by 1/2 and syrup is coating the back of a spoon when dropped in cold water or until a candy thermometer reads 230 degrees F.
Using a stand or hand mixer, beat the egg whites until soft peaks form. Slowly add 1/2 of the hot syrup and continue beating until firm peaks form and the meringue has cooled.
With a spatula, gently fold in 1/4 of the meringue into the almond mixture. Continue folding the meringue until completely incorporated. The mixture will be shiny and smooth.
Fit a piping bag with a 3/8-inch/1 cm round tip. Pipe the batter onto the baking sheets. Tap the underside of the baking sheet to remove air bubbles. Let dry at room temperature for 1 hour to allow skins to form.
For the butter cream:
Bring the water and sugar to a boil and cook it until it reaches 242 degrees F on a candy thermometer, approximately 4 minutes.
Using a stand or hand mixer, pour in egg yolks and crack in one extra egg. While beating, gradually pour the remaining hot syrup on the egg yolks. Beat until cooled, light and fluffy, approximately 10 minutes.
Add the butter and continue beating until smooth. Add the vanilla. Put aside.
Preheat the oven to 275 degrees F.
Bake the macarons for 20 minutes. Rotate the baking sheet after 10 minutes for even baking.
Remove the macarons from the oven and transfer parchment to a cooling rack.
Pair the macarons of similar size, and pipe about 1/2 teaspoon filling onto one of the macarons. Top with the other macaron to sandwich the filling.