Leek, smoked cheddar and mustard rarebits

Method

1. Pour the ale into a pan over a high heat and bring to the boil. Bubble until the ale is reduced to 150ml, then take off the heat and set aside.
2. Put a large heavy-based pan over a medium heat. Add the olive oil and the chopped chestnuts, then season with salt and pepper. Fry for 4-5 minutes, stirring, until the chestnuts start to crisp around the edges. Use a slotted spoon to lift them out onto a plate lined with kitchen paper.
3. With the pan still on the heat, add the butter and, when it’s foaming, add the sliced leek and garlic, then season with salt and pepper. Cook, stirring regularly, for 4-5 minutes, then stir in the flour. After a minute add the reduced ale and mix well using a wooden spoon. When the mixture starts to thicken and bubble, add the mustard, grated cheese and chopped parsley, then taste and season. Cook, stirring all the time, until the cheese has completely melted. Take the pan off the heat (see Make Ahead).
4. Heat the grill to medium. Toast the bread on both sides, then spoon over the cheesy leek mixture, spreading it out to reach the edges of the toast. Put the rarebits back under the heat and grill until bubbling and blistered. Serve straightaway, scattered with the chestnuts.