Pierre Desfontaines is credited with creating the French macaroon at the beginning of the 20th century by marrying two meringue shells with a filling. These little cookies have an exceptional texture; they are crunchy on the outside and buttery soft on the inside. Macaroons are often dyed pretty colors to match flavors as unusual as rose, bergamot, peach, licorice and currant. Some pastry shops, such as Ladurée in Paris, invent new flavors every season, but pistachio is always a classic.
Make the Macaroons
Preheat the oven to 300 degrees Fahrenheit. Line two sheet pans with parchment paper.
Grind 1 cup pistachios, 2 cups powdered sugar and 1/8 tsp. of salt in the food processor until the nuts are ground fine as dust. Sift the mixture with a flour sifter.
Pulverize the granulated sugar in a coffee grinder until it becomes like powder. Set aside.
Prepare a French meringue by whisking the egg whites and 1/8 tsp. of cream of tartar in a stand mixer until they're frothy. Add the pulverized sugar and 3 drops of green food coloring. Continue whipping the meringue until it is very stiff.
Using a rubber spatula, fold the nut mixture into the meringue until they're fully combined. Do not overmix the batter or it will become runny.
Pipe the meringue into 1-inch rounds with a No. 4 round tip inserted into a piping bag. Hold the piping bag vertical without moving it while squeezing the batter into even circles. Fill both sheet pans with cookies.
Let the piped macaroons rest for 30 minutes before baking. The batter will form skin that will prevent the surface of the cookies from cracking while they're in the oven.
Bake the macaroons for 15 to 20 minutes, or until the surface is hard. Do not let the cookies turn golden--this is a sign that they are overdone. Let them cool completely on the sheet pans.
Prepare the Filling
Grind the remaining 1/2 cup of pistachios very finely in a coffee grinder or food processor.
Mix the ground pistachios, 1 2/3 cups of powdered sugar, 1/2 cup of butter, 1/8 tsp. of salt and 1 tsp. of milk together in the stand mixer fitted with the paddle attachment. Scrape down the sides of the bowl with a rubber spatula.
Add the remaining 3 drops of green food coloring to the butter cream. Whip until it's light and fluffy.
Assemble the Macaroons
Scoop the butter cream into the pastry bag fitted with a No. 4 round tip.
Pipe a small amount of frosting onto the flat side of one macaroon and gently sandwich it with another macaroon.
Refrigerate the cookies 24 to 36 hours before serving. The recipe makes 20 to 25 small cookies.