For the macarons:
225 gm confectioners’ sugar
60 gm blanched, slivered almonds
65 gm pistachios
3 egg whites (about 100 gm), aged 1 day at room temperature
25 gm granulated sugar
Green powdered food coloring (optional)
For the ganache:
8 oz. bittersweet or semisweet chocolate, finely chopped
¾ cup heavy cream
2 tbsp. unsalted butter, at room temperature
1 tsp. almond extract (optional)
To make the cookies, combine the confectioners’ sugar, almonds, and pistachios in the bowl of a food processor. Process until the nuts are very finely ground and the mixture is well blended. In the bowl of an electric mixer fitted with the whisk attachment, whip the egg whites on medium-high speed until foamy. Gradually add the granulated sugar and continue beating until the egg whites are glossy and hold stiff peaks. Mix in the powdered green food coloring, if using. (Start with only a little bit at a time. Remember, you can always add more but you can’t take it away.) Add the ground nut/sugar mixture to the mixing bowl and gently fold in to the egg whites using a wide spatula. The mixture should remain shiny and flow easily.
Transfer the batter to a pastry bag fitted with a plain round tip. Pipe rounds (approximately 1 inch in diameter) onto baking sheets lined with silicone baking mats. Let rest for 20 minutes. Preheat the oven to 315˚ F. When they are finished resting, baking for 12-15 minutes. Let cool completely before carefully removing from the baking sheets.
To make the ganache, place the chopped chocolate in a medium bowl. Set aside. Heat the cream in a small saucepan, just to boiling. Immediately remove from the heat and pour over the chocolate. Allow to sit for 3 minutes. Using a whisk in small circular motions, combine the cream and chocolate until a thick ganache forms. Whisk in the butter until well incorporated and smooth. Stir in the almond extract, if using. Let sit at room temperature, stirring occasionally, until firm enough for piping. (Speed the process up by chilling in the refrigerator or freezer, whisking every 10 minutes or so.)
To assemble the cookies, match up the cookie shells by size. Pipe a dollop of ganache onto the flat surface of one cookie of each pair. Top with the other cookie and sandwich together, pressing gently to push the ganache to the edges of the cookies.