Potato Gratin with Ham & Cheese

Ingredients

• 1.2kg potatoes, peeled and thinly sliced (3mm)
• 1 small onion, thinly sliced
• 6g fresh thyme leaves (optional)
• 200g cooked ham, sliced or chopped
• 40g plain flour
• Salt and black pepper, to taste
• 600ml warmed milk
• 40g butter
• 200g grated cheddar (reserve some for the top)
• 1 tsp Dijon mustard
• 1/4 tsp ground nutmeg
• Crusty sourdough bread, to serve
• Dressed green salad, to serve

Method

1. Heat the oven to 180°C (fan 160°C) and butter a 20x30cm ovenproof dish generously. Slice the potatoes a steady 3mm thick — any thicker and they won't cook through in the time the top takes to brown.
2. Melt the butter in a saucepan over a medium heat until foaming, stir in the flour and cook for 1 minute until it smells biscuity — that's the raw flour cooking out. Gradually whisk in the warmed milk a splash at a time, letting each addition come together before the next, then simmer for 3–4 minutes, stirring, until thick enough to coat the back of a spoon.
3. Off the heat, stir in most of the grated cheddar, the Dijon and the nutmeg until glossy. Season the sauce generously with salt and pepper, then taste it — it should taste a touch over-seasoned on the spoon, because the potatoes are bland and will soak it up. Adjust now, not at the table.
4. Layer a third of the potatoes across the base of the dish, season the layer with a pinch of salt and pepper, scatter over half the onion and half the ham, then spoon over a little sauce so every slice is properly coated. Repeat with another seasoned layer and finish with a neat top layer of potatoes.
5. Pour the remaining sauce over the top so it seeps between the slices — it should come close to the top of the potatoes. Scatter over the reserved cheddar and the thyme leaves if using.
6. Cover loosely with foil and bake for 45 minutes, then uncover and bake for a further 15 minutes until the top is deeply golden and bubbling at the edges and a skewer slides through the potatoes with no resistance. If the top is pale, push it under a hot grill for 2 minutes — watch it, cheese goes from golden to scorched fast.
7. Rest for 10 minutes so the layers settle and slice cleanly — straight from the oven it slumps, rested it holds.
8. Scatter the parsley over the gratin, bring a squeeze of lemon to each plate to cut the richness, and serve with the green salad or buttered peas alongside.