Ingredients

Equipment Needed

• •23cm pie dish
• •Rolling pin
• •Large mixing bowl
• •Wide frying pan or sauté pan

Instructions

1. 1

   Make the pastry

   Put the flour and salt in a large bowl. Add the cold butter and rub it in with your fingertips until the mixture looks like rough breadcrumbs. Some larger pieces of butter are fine. They'll make the pastry flaky. Add the water a tablespoon at a time, mixing with a knife, until the dough just comes together. Don't overwork it. The moment it holds in a ball, stop. Wrap in cling film and rest in the fridge for at least thirty minutes. The pastry needs to relax. So do you.

   Cold hands and cold butter are the whole secret to good pastry. If the kitchen is warm, run your hands under cold water before you start. And keep that butter in the fridge until the last moment.
2. 2

   Cook the onions slowly

   While the pastry rests, slice the onions thinly and put them in a wide pan with the butter over a low heat. This is not a five-minute job. Give them twenty-five to thirty minutes, stirring now and then, until they've gone from sharp and white to soft, golden, and deeply sweet. The kitchen will smell extraordinary. If they start to catch, turn the heat down. If you rush them, you'll taste it. Season well with salt and pepper, then take them off the heat and let them cool slightly.

   The onions should be completely soft and sweet, with no bite left. Taste one. If there is any sharpness, they need more time. Trust your tongue, not the clock.
3. 3

   Build the filling

   Grate the cheddar and stir it through the warm onions. The cheese should soften and start to melt into them without disappearing entirely. You want pockets of cheese that will go molten in the oven. Add the mustard powder if you're using it. It won't make the pie taste of mustard. It will just make the cheese taste more like cheese.

4. 4

   Assemble the pie

   Set the oven to 200C (180C fan). Cut the pastry roughly in two, one piece slightly larger than the other. Roll the larger piece out on a floured surface until it's big enough to line a 23cm pie dish with a little overhang. Don't worry about neatness. Spoon the filling in and spread it level. Roll out the remaining pastry for the lid, lay it over the top, and press the edges together to seal. Trim the excess and crimp with a fork or your thumb. Cut a small slit in the centre to let the steam escape. Brush the top with beaten egg.

   If the pastry tears while rolling, just patch it. Press the edges together with wet fingers and carry on. It's going to taste exactly the same. We're only making dinner.
5. 5

   Bake until golden

   Bake for thirty-five to forty minutes, until the pastry has gone a deep, confident gold and the pie feels firm when you press the top gently. You'll hear the filling bubbling through the steam hole. Let it rest for ten minutes before cutting. The filling needs a moment to settle, and the first slice will come out cleaner for the wait. Eat it warm with whatever feels right. A heap of baked beans. Some pickled onions. A green salad if you're feeling virtuous. A mug of tea regardless. Your kitchen, your rules.

Chef Tips

• •Use the strongest cheddar you can find. A mild cheddar in a pie like this is a missed opportunity. You want something with enough character to stand up to the sweet onions and hold its own inside all that pastry. A proper mature farmhouse cheddar, the kind that crumbles when you try to slice it, is what you're after.
• •The onions are the whole point. If you cook them for ten minutes and call it done, you'll have a pie that tastes of raw onion and regret. Thirty minutes over a low flame turns them into something else entirely: sweet, golden, almost jammy. That transformation is the difference between a good pie and one worth writing down.
• •This pie is as good cold as it is warm. Wrap a wedge in paper and take it to work. Eat it on a bench somewhere. There are few better packed lunches, and I've spent a long time looking.

Advance Preparation

• •The pastry can be made the day before and kept wrapped in the fridge. Let it sit at room temperature for ten minutes before rolling, or it will crack and fight you.
• •The onion filling can be cooked ahead and refrigerated overnight. Stir the cheese through when you're ready to assemble, while the onions are at room temperature.
• •The assembled, unbaked pie freezes well for up to a month. Bake from frozen, adding ten to fifteen minutes to the cooking time, and brush with egg wash before it goes in.

Frequently Asked Questions

Nutrition Information

1 serving (about 225g)