Bring the cream cheese to room temperature, then butter and line a 20cm springform pan with parchment paper.
To prepare the base, crush the Digestive biscuits to crumbs and mix with the cocoa powder and salt. Stir in the melted butter and mix until combined. Press the mixture onto the bottom of the springform pan. Refrigerate the crust for 30 minutes.
Meanwhile, prepare the raspberry coulis: cut the raspberries in half and cook them for 5 minutes in a small pot with the sugar. Strain well the mixture through a fine mesh strainer.
To prepare the cheesecake filling, put the gelatine leaves into a bowl with cold water for 10 minutes. Meanwhile, whisk together cream cheese, ricotta cheese and icing sugar. At this point, dissolve the gelatine into 2 tbsp of heated heavy cream. After waiting 2 minutes, quickly incorporate the gelatine inside the ricotta cream. Finally, whip the cream and add it gently to the mixture.
Pour half the filling into the springform pan, then spread the raspberry coulis remaining 2 cm inside the edge. Cover with the rest of the filling, level the surface and leave the cake in the refrigerator for at least 4 hours. After removing the cheesecake from the pan, decorate with chopped dark chocolate and fresh raspberries.