Step 1

Line 2 baking sheets with parchment paper.

Step 2

Grind 1 cup of the confectioners' sugar, the hazelnuts, and cocoa in a food processor until powdery, about 3 minutes. Sift mixture through a medium mesh strainer onto a piece of parchment paper, then discard any large pieces of nuts that didn't come through the strainer.

Step 3

With an electric mixer, beat the egg whites and salt until they hold firm but not dry peaks, about 2 minutes. Gradually add the remaining 1 cup confectioners' sugar, a tablespoon at a time, scraping down the sides of the bowl as needed; this can take up to 3 minutes. Beat for an extra 30 seconds until the peaks are firm and shiny but still not dry. Fold the nut mixture gently into the egg whites with a large rubber spatula. Transfer mixture into a large piping bag fitted with a 1/2-inch plain piping tip. Pipe 32 2-inch by about 1/3-inch thick rounds, evenly spaced, on each of the prepared pans. Set aside to air dry for 30 minutes before baking.

Step 4

Meanwhile make the filling: Put chocolate in a medium heatproof bowl. In a small saucepan, bring cream, with espresso powder mixed in, to a boil. Pour cream over chocolate and shake bowl gently so cream settles around the chocolate. Set mixture aside until the chocolate is soft, about 5 minutes. Whisk gently until smooth, taking care not to incorporate too many air bubbles. Cool at room temperature until set up.

Step 5

Preheat oven to 325 degrees F.

Step 6

Bake macaroons until set and puffed, about 18 to 20 minutes. Take care not to overcook the macaroons or they'll crack. Cool cookies for 5 minutes then gently peel from paper. Let cool completely.

Step 7

Spread 1 teaspoon of mocha filling on a cookie and sandwich 2 cookies together.