Mix the mascarpone, natural yoghurt, sugar, lemon juice and the grated lemon zest together. Carefully fold in the whipped cream.
Now put 1/4 of the grapes in a large bowl. Spread 1/4 of the amaretti over it, drizzle with white wine or juice of your choice and pour some of the mascarpone cream over it. Alternately layer the remaining ingredients until they are used up - save a few amaretti for garnish. Finish with mascarpone cream. Chill until ready to eat. Sift some cocoa powder over it right before consumption and garnish with the set aside amaretti.