To make the pastry, put the shortcrust dough and cheese in the bowl of a food processor. Pulse until combined, breaking up any lumps. Add the parsley and pulse for a few seconds more until mixed. Bring together in a ball and tip out onto a lightly floured surface.
Roll out the dough to a circle large enough to line a 22cm (8 1/2in) deep pie dish. Trim and crimp the edges; chill for 30 minutes.
Meanwhile, put the potatoes in a large pan of water. Bring to the boil, then simmer for 10-15 minutes, until tender. Remove from the heat and drain. Leave to cool, then roughly slice. Preheat the oven to gas 4, 180°C, fan 160°C. Put a baking sheet on the middle shelf to heat up.
Meanwhile, microwave, steam or boil the spring greens following the packet instructions, until wilted. Leave to cool a little, then squeeze out the excess water. In a mixing bowl, whisk the eggs, cream, mustard and ricotta until combined; season. Cut the asparagus in half and set the spears aside. Dice the stalks into 1cm (1/2in) chunks and add to the ricotta mixture with the spring greens, peas, potatoes and most of the spring onions. Scatter over most of the cheese and mix well.
Line the chilled pastry base with the polenta, breadcrumbs or almonds. Tip in the filling, pressing down with the back of a spoon until tightly packed. Arrange the reserved asparagus spears on top, then scatter over the remaining spring onions and cheese. Bake on the preheated baking sheet for 45 minutes, or until the filling is set and the pastry golden. Leave to stand for 15 minutes before serving.
Tip: As the pie contains potatoes, serve with roasted parsnips, buttered carrots and Savoy cabbage, plus a dollop of wholegrain mustard.
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