Heat oven to 200C/180C fan/gas 6 and put a baking sheet in the oven to heat up. Lightly dust a surface with flour, then roll out the pastry into a circle. Use to line a 22cm tart tin (3cm deep) with a removable base. Trim away any excess pastry that hangs over the top and chill while you make the filling.

Heat the butter in a frying pan, add the leek in a single layer and fry for a minute, then add 50ml water and cover with a lid. Cook over a low heat for 4 mins (check it doesn’t dry out). Whisk the cream and egg together, then mix in the spinach and peas.

Tip the pea mixture into the base of the tart and arrange the leek on top. (If you don’t want the leeks on top, then stir them through the pea mixture.) Break the mozzarella pearls in half and dot them over the tart. Put the tart on the baking sheet and bake for 30 mins, or until the filling is cooked through. Leave to rest for 5 mins before cutting.