Pastry: Sift the flour into a large bowl, add the butter and rub in with your fingertips until the mixture resembles fine breadcrumbs. If you have a food processor you can use that and it is a lot faster.

Stir in the salt, then add 2-3 tablespoons ice water and mix to a firm dough. (I think I had to use almost 6 tablespoons before the dough started to come together).  Here's a video if you want to watch someone making shortcrust. Knead the dough briefly and gently on a floured surfce. Wrap in plastic wrap adn chill while preparing the filling. For best results make sure the butter is very cold.

Preheat oven to 390°. Put the mascapone or cream cheese in a food processor with the watercress, arugula, and spinach and process until you have a creamy green puree. Season with salt and pepper (I added 1/2 teaspoon of dill weed.)