Mocha almond roulade with rum cream

Sift the first quantity of castor sugar with the cocoa and coffee granules into a small bowl.
Beat egg yolks until thick and pale, then gradually beat in sugar mixture. Beat for a further 2 minutes. Fold in ground almonds, flour and baking powder (mixture will be very stiff).
Whisk egg whites in a large bowl until frothy. Add cream of tartar and continue to whisk until eggs form soft peaks. Whisk in remaining castor sugar, 15 ml (1 tbsp) at a time, and continue whisking until stiff and shiny.
Fold some of the egg whites into the egg yolk mixture to soften it, then fold egg yolk mixture into meringue, gently but thoroughly. Pour into a buttered, parchment-lined, 30 x 40 cm baking pan and spread evenly.
Bake at 180 ºC for 10 to 15 minutes, or until cake starts to shrink from sides of pan. Invert cake onto a clean tea towel sprinkled with icing sugar. Leave to cool, then tear off paper in lengthways strips.
Beat cream with icing sugar and rum until it forms stiff peaks. Spread cream over cake to within 5 mm of edges. Roll up tightly, lengthways, using towel as a guide and finishing with seam side down. Chill for at least 1 hour.
Transfer to a serving platter and sift icing sugar over. Slice diagonally to serve.