Heat oven to 190C/170C fan/gas 5. Roll out the pastry and line a 28cm tart tin. Chill for 30 mins. Meanwhile, make the pesto. Place the watercress, pine nuts, Parmesan, olive oil and lemon juice in a food processer and blitz to a thick sauce. Season to taste and set aside.
Cook the broad beans for 1 min in a pan of boiling water. Drain and refresh under cold water, then peel off the outer layer. Place the peeled beans to one side.
Line the tart with greaseproof paper and fill with baking beans. Bake for 10 mins, remove the paper and beans and cook for 15 mins more until light golden. Remove from the oven and reduce temperature to 180C/160C fan/gas 4. Set aside the pastry while you make the filling.
Mix the ricotta and creme fraÃ®che with the beaten eggs. Stir in the cheese and lemon zest, then fold in the broad beans, taking care not to break or crush. Spread over the tart case, then place artichoke hearts on top. Bake for 30-40 mins, remove and serve warm with the watercress pesto.