Combine icing sugar and almond flour together in a bowl. Add a squeeze of lemon juice and a small dash of egg whites and mix well. Heat sugar and water to 118 degrees C. Whisk egg whites – to soft peak and slowly pour in melted sugar. Beat until cool. Vigorously beat in ½ the meringue mix into almond flour mix to form paste then fold in the remainder of the meringue mix. Pipe onto a non-stick mat or greased parchment paper. Leave to dry for 2 hours. Bake at 160 degrees C for 12 minutes, turning the tray halfway through baking time to ensure even baking. Remove from the oven and allow to cool completely.
Melt chocolate in a bowl over gently simmering water. Mix sugar and egg yolks then add the cream. Whisk egg whites and fold into the mixture. Pour the chocolate mix into a piping bag and refrigerate until later.
Pipe the mousse onto the macaroons and gently sandwich together.