Start by preparing the biscuit base: finely mix the dry biscuits and mix in the melted butter. Pack this mixture into the bottom of a 22cm springform pan (to facilitate demoulding). Go up a little on the edges to be able to garnish the pie. Place in the freezer for 30 minutes.
For the garnish: whip the heavy whipped cream with half the icing sugar. Relax the mascarpone with a fork then add it to the whipped cream with the rest of the icing sugar. Whisk again to obtain a homogeneous creamy mixture. Finish by incorporating the lemon juice and zest. Place in the refrigerator while waiting.
To prepare the blackberry juice: mix about ten blackberries with 1tsp icing sugar. Filter through a fine sieve to extract only the liquid (if it is too thick, add a little water).
Decorate the pie with a little blackberry juice and the blackberries (on one side like me or by placing them all over the pie).