A food processor will make light work of chopping the mushrooms and grinding the walnuts. Throw the walnuts in a food processor, grind them as finely as you can, then tip out into a bowl.

Break up the mushrooms, add them to the processor, chop until pea-sized and put to one side (alternatively, chop them by hand).

Put the oil in a large frying pan on a medium heat and, once it’s hot, add the mustard, cumin and nigella seeds. When the seeds start to wriggle in the hot oil, add the onion and saute, stirring, for about eight minutes, until soft and starting to brown.

Add the ginger, garlic and chillies, and fry, still stirring, for a further five minutes, until the onions look like dark jewels.

Add the chopped mushrooms – don’t worry if they come right to the brim of the pan, because they’ll reduce in volume soon enough.

Gently fold the mix for about seven minutes, then add the salt and pepper, and cook for another 15 or so minutes, until all the liquid has evaporated; there should be only the tiniest trace left in the bottom of the pan, otherwise you’ll have soggy samosas.

Stir in the ground walnuts, cook, stirring, for three minutes more, then take off the heat and leave to cool while you get a samosa station ready.

Heat the oven to 220C (200C fan)/425F/gas 7 and line two baking trays with greaseproof paper.

Unroll one sheet of filo pastry and lay it on a work surface so that one long side is facing you. Brush lightly all over with melted butter, then top with a second sheet of filo. Cut the stack of sheets in half across the middle from top to bottom, then cut each half horizontally into three, so you end up with six roughly 8½cm x 23cm strips.

Make a triangular cone shape at one end of one strip, place 30g of the filling inside it, then, working your way along the strip, fold the pastry repeatedly up and over the filling, following the original triangular shape. When you get to the end of the strip, stick the final bit down using a little melted butter as the glue.

Pop the samosa on a tray and repeat twice more with four of the remaining filo sheets.

When you get to the seventh and last sheet of filo, cut it in half from top to bottom, brush with butter and lay one half on top of the other. Cut this horizontally into three strips as above, fill with the last of the filling, and fold up as before.

Brush both sides of the samosas with the last of the butter, arrange them on the trays in a single layer and bake for 15 minutes, until golden brown. Serve with a chutney of your choice.