Blanch the peas in salted water for 30 seconds. Drain and refresh under cold water. Blanch the fava beans the same way and pod them: squeeze each broad bean delicately between your thumb and index to pop them out of their membrane. Set aside.

Pan-fry the onions and carrots in the olive oil for 10 minutes, until the carrots are tender. Add the chopped zucchini and cook for 2 to 3 minutes. Add the peas, fava beans and chopped zucchini. Season well and cook for a minute. If the mixture is too wet, place it under a hot grill for a few minutes. Leave to cool.

Mix the cooled vegetables with the ricotta, egg yolk, ½ cup of Grana Padano PDO cheese and lemon zest until well blended. Season nutmeg, salt and freshly ground black pepper.

Preheat the oven to 400˚. Lightly beat the egg with a pinch of salt. Cut the puff pastry into 8 (12x23cm) rectangles (you will have some left-over pastry). Line two large baking trays with baking paper and lay two pastry rectangles on each one. Spread a quarter of the vegetable and ricotta mixture on top of each rectangle, leaving a 1 inch border all around.

Brush the border with beaten egg and lay a second rectangle of pastry over the top. Seal the edges by pressing down with a fork. Poke the top, brush with egg and sprinkle with remaining Grana Padano PDO cheese. Repeat for the other three pies. Bake the pies for about 30 minutes. They should be well risen and golden. Leave to cool.

Makes 4 pies, 10-12 servings.