Pre heat oven to 1800C . Line a high wall tart pan with the pastry sheets and trim any excess. Blind bake the pastry with baking beads for 10 minutes. Remove beads and cook a further 5 minutes. Remove from and set aside to cool.
Melt the chocolate in a heatproof bowl over a pan of simmering water. Stir until smooth, remove form the heat and cool completely. Once cooled, mix the chocolate and ricotta until fully combined.
Whip the cream to medium peaks. Fold a little of the ricotta mix to incorporate, and then fold the remaining cream.
To serve spoon the chocolate filling into the pastry case, then top with blue berries.
This tart can be made ahead and refrigerate till needed.