Using the whisk on a hand mixer, beat the sugar, egg yolks and orange zest until the mixture becomes lighter in colour. Whisk the mascarpone until smooth, stir in. Beat the egg whites with the salt until stiff, add the sugar, continue beating until the egg whites turn glossy. Carefully fold the egg whites into the mixture using a rubber spatula, chill.
Mix the coffee, amaretto and sugar until the sugar has dissolved, leave to cool.
Place half of the sponge fingers (sugar side down) in the dish, drizzle with half of the liquid. Spread half of the mascarpone mixture on top. Dip the remaining sponge fingers into the liquid, place on top. Cover with the remaining mixture. Cover and chill for approx. 2 hrs. Dust with cocoa powder.