Preheat oven to 300°F. Line 2 jelly roll sheets with parchment paper or Silpat. Prepare 2 piping bags with a 1/2 inch round tip.

Separate egg whites from egg yolks, being careful not to contaminate the whites with the yolks. Measure out 100 grams of egg whites (about 3 eggs), cover with plastic and let stand at room temperature overnight. OR – microwave for 20 seconds, in 5 second intervals, mixing after each stop.

In a bowl of a food processor, combine 200 grams powdered sugar, 50 grams almond flour and 50 grams peeled pistachios. Pulse to combine, about 20 seconds. Then pulverize for about 3-4 minutes until a very fine mixture forms, stopping several times to scrape the sides. Set aside.

Start whipping the egg whites with a pinch of salt. Once foamy, start adding the granulated sugar and whip until stiff peaks form. Add the food coloring. Mix to somewhat incorporate.

Add 1/2 the powdered sugar mixture and with very quick mixing motions, make about 5-6 swirls with a spoon to combine the meringue with the powdered sugar mixture. Add the other 1/2 of the dry ingredients and carefully fold them in until fully combined. Take care not to overmix. Stop when the batter falls in a thick ribbon and disappears in about 30 seconds. (OR when you're able to "draw" an 8 with the batter falling off the spatula)

Fill the piping bag with batter and pipe out 1 inch circles onto parchment paper about 1.5 inches apart. Sprinkle the piped macarons with chopped pistachios. Slide the first sheet in the oven and bake for 10-12 minutes, until the tops are dry to the touch and lift off cleanly off the parchment paper. 

For the second batch, either wait until the baking sheet cools to room temperature or use a different one and also bake for 10-12 minutes. Baking times might vary depending on the oven, so go by how the macarons come off the parchment paper.

Remove from the oven and let cool.

Carefully peel off the baked macaron shells by lifting them off the parchment paper.

Combine 6 tbsp sugar and 2 tbsp water in a small saucepan and cook the syrup to soft ball stage (that’s when a drop of syrup, dropped into a glass of water can be formed into a soft ball). 

Whip 100 grams butter for about 3 minutes.

With a stand mixer, whip 1 egg to soft peaks. Without stopping the mixer, carefully pour in the syrup between the whip attachment and the bowl. Whip until the bowl feels cool to the touch. 

When the egg has cooled, without stopping the mixer add 1 the whipped butter 1 tablespoon at a time. Next, add the vanilla extract. The mixture might become runny and might look curdled, continue to whip and it will come together into a smooth buttercream. Lastly, add the chopped pistachios if you wish.

Fill the pastry bag (or a ziplock bag) with the French buttercream. 

Pair the cookies by size and sandwich them with the buttercream.

Let the macarons sit in a tightly closed container 24 - 48 hours at room temperature or in the fridge OR until the middle of the cookie is almost fudge-like and the tops are still crispy. Bring to room temperature before serving.