Hazelnut Macaron Sandwiches
4 egg whites, at room temperature
1/4 tsp. cream of tartar
1/4 cup superfine sugar
1 tsp. vanilla extract
1 cup toasted, skinned and ground hazelnuts
2 cups confectioners’ sugar, sifted
About 2/3 cup ganache filling, refrigerated until cool and thick enough to spread
Line 2 rimless baking sheets with parchment paper. Have ready a third rimless baking sheet, unlined.
In the bowl of an electric mixer fitted with the whisk attachment, combine the egg whites and cream of tartar and beat on medium speed until the whites begin to thicken. Increase the speed to medium-high and beat just until soft peaks form. Slowly add the superfine sugar and continue to beat until stiff, shiny peaks form. Beat in the vanilla until blended. Using a rubber spatula, fold in the hazelnuts and confectioners sugar until incorporated.
Scoop the mixture into a pastry bag fitted with a 1/2-inch plain tip. Pipe mounds 1 1/2 inches in diameter onto the prepared baking sheets, spacing the mounds 1 inch apart. With a damp fingertip, gently smooth any pointy tips. Let the cookies stand, uncovered, at room temperature for 35 to 45 minutes.
Preheat an oven to 350°F.
Bake the cookies, 1 sheet at a time, putting the cookie-filled baking sheet on top of the unlined baking sheet. (This insulates the top baking sheet so the cookie bottoms do not darken too much.) Bake until the tops and bottoms are firm and golden, 10 to 13 minutes.
Remove the baking sheet from the oven, carefully lift the parchment, one end at a time, and sprinkle about 2 Tbs. water under the paper. Be careful that the steam does not burn you and that water does not splash on the cookies. (The steam loosens the cookies from the paper.) After 3 minutes, slide the parchment paper off the baking sheet, peel the cookies from the paper and transfer them to wire racks to cool completely.
Turn half of the cookies bottom side up. Spread a thin layer of the ganache filling (about 1 rounded tsp.) over the cookie bottoms. Press a plain cookie, bottom side down, onto the ganache. Store the cookies in an airtight container at room temperature for up to 3 days. Makes about 24 cookies.