Serves: 16 sandwiched biscuits1) Line 2 baking sheets with parchment paper.
4) Gradually add the remaining icing 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.
5) 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-cm plain piping tip. Pipe 3 3-cm by about 0.5cm thick rounds, evenly spaced, on each of the prepared pans. Set aside to air dry for 30 minutes before baking.
6) 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.
7) 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.
8) Preheat oven to 160°C. 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 five minutes then gently peel from paper. Let cool completely.
9) Spread one teaspoon of mocha filling on a cookie and sandwich two cookies together.