Step 1

Put the oil, onions, curry powder, chilli flakes (if using) and two-thirds of a teaspoon of salt in a medium saucepan and put it on a medium-high heat.

Step 2

Cook, stirring frequently, for 10 minutes, until the onions are lightly caramelised, then add the butter and cook, still stirring often, for 15 minutes more, until the onions are a deep golden brown; add a splash or two of water, if need be, to stop them catching.

Step 3

Stir in the spinach, tomatoes and coconut, and cook, stirring, for another five minutes, until the spinach has wilted. Off the heat, stir in the coriander and mozzarella, and leave to cool.

Step 4

On a lightly floured work surface, roll out one of the pastry sheets into a roughly 40cm x 30cm rectangle that’s about 1mm thick. Using a 14cm round pastry cutter (or a similar-sized bowl), cut out four circles from the sheet. Bring together the offcuts, roll out again, then cut out a fifth circle. Repeat with the second pastry sheet, so you have 10 pastry circles.

Step 5

Spoon 55-60g of the spinach mix just off centre on to each circle. Lightly brush water around the edges of the filling, then fold over the pastry and press around the edges to seal; if you like, crimp them with a fork. Put the pies on an oven tray lined with greaseproof paper, then refrigerate for 30 minutes, until the pastry is good and firm.

Step 6

When you want to bake the pies, heat the oven to 220C (200C fan)/425F/gas Brush the egg yolk liberally over the top of each pie. Using a serrated knife, cut three 2cm-long diagonal slits into the top of each. Sprinkle over the nigella seeds, if using, then bake for 25 minutes, until golden brown.

Step 7

Take the tray out of the oven, put on a rack for no more than five minutes, to cool slightly, then serve hot.