Harissa & Gruyère Gratin

Ingredients

• 1 kg floury potatoes, thinly sliced
• 2 banana shallots, finely sliced
• 4 garlic cloves, finely chopped
• 2 tbsp harissa paste
• 300 ml double cream
• 200 ml whole milk
• 150 g Gruyère, grated
• 1 tsp thyme leaves
• 1 tbsp olive oil
• Fine salt and black pepper

Method

1. Heat the oven to 180°C fan. Rub a deep 25 x 35 cm baking dish with the olive oil.
2. Whisk the double cream, milk, harissa, garlic and thyme together with 1 teaspoon of salt and plenty of black pepper. Taste a drop of the mixture. It should be assertively seasoned because a kilo of potatoes will soften both the chilli and the salt.
3. Layer the potatoes and shallots in the dish, keeping the slices mostly flat so they cook at the same rate. Pour over the harissa cream, pressing the top layer down until the liquid reaches it. Cover the dish tightly with foil.
4. Bake for 50 minutes, then push a knife into the centre. It should meet very little resistance. If the potatoes are still firm, cover and give them another 10 minutes before adding the cheese; cheese cannot rescue undercooked potato.
5. Remove the foil, scatter the Gruyère evenly over the top and bake uncovered for 30 to 35 minutes, until the surface is deeply golden and the cream bubbles thickly around the edges.
6. Rest for 15 minutes before serving. The sauce thickens as it stands, so cutting straight away gives you a puddle instead of a gratin.