Preheat the oven to 180°C and place a baking tray on the middle shelf to heat up. Make the pastry by placing the diced shortcrust and Cheddar into a food processor.
Pulse until combined, ensuring that there are no large lumps. Add the parsley and pulse for a few more seconds until fully mixed. Bring together into a ball and turn out onto a lightly floured work surface.
Roll out the dough to a circle large enough to line a 22cm pie dish, then line the dish and trim the edges. Place in the fridge to chill for at least 30 minutes.
Put the potatoes in a large pan of salted water and bring to the boil. Simmer for around 15 minutes or until tender. Drain and leave to cool before roughly slicing.
Bring a medium saucepan of salted water to the boil and add in the spring greens. Cook for 6-8 minutes or until tender before adding in the watercress for the last 30 seconds of cooking. Drain and run over cold water to cool.
Squeeze out any excess water and set aside.
In a mixing bowl, whisk together the eggs, cream, mustard and ricotta until combined. Season well with salt and pepper.
Cut the asparagus tips off and reserve, then cut the stalks into 1cm chunks and add to the ricotta mix along with the greens, peas, and potatoes. Reserve a little of the spring onions and cheese for later then add the rest to the mixture and combine well
Take the pastry base from the fridge and line with the breadcrumbs before tipping in the ricotta mixture, pressing down with a spoon until tightly packed. Arrange the asparagus tips on top, then scatter over the remaining cheese and spring onions.
Place on the pre-heated baking tray and bake in the centre of the oven for 45 minutes, or until the filling is set and the pastry is golden. Leave to stand for 15 minutes before serving.