Mix the lemon juice, most of the zest and the limoncello together. Pour the cream into a large bowl and softly whip with the sugar. Srizzle in the lemon mixture and whisk until incorporated.
Divide between 6 small glasses and refrigerate for at least an hour. Just before serving, put 6 biscuits in a plastic bag. Crush with a rolling pin and sprinkle over each dessert with a little lemon zest. If you like, serve each with a biscuit.