Heat oven to 200C/180C fan/gas 6. Heat the oil in a large saucepan, add the onion with a pinch of salt and gently fry until softened, so around 8-10 mins. Stir in the garlic and nutmeg, cook for a minute, then add the greens along with a splash of water. Stir until wilted, so around 3 mins, then stir in the mascarpone, parmesan and a squeeze of lemon juice. Season well and tip the mixture into the base of a 20cm pie dish.

Unroll the puff pastry and brush the edges of the pie dish with water. At this point, you can do what you want with the pastry – you could lattice it, crimp the edges, add decoration, or just stick it on as is. Seal it to the edge of the pie dish, brush with the beaten egg and bake for 35 mins until risen and golden. Allow to cool for 10 mins before serving.