French Onion and Gruyère Potato Gratin

Ingredients

• 900 g floury potatoes
• 3 large onions
• 150 g gruyère cheese
• 300 ml double cream
• 150 ml whole milk
• 30 g butter
• 2 garlic clove
• 5 g fresh thyme
• 1 tsp Dijon mustard

Method

1. 1

   Preheat the oven to 180°C (fan 160°C). Thinly slice the onions and cook in butter over a low heat for 20 minutes, stirring often, until deeply golden and caramelised.

2. 2

   Meanwhile, thinly slice the potatoes (a mandoline is ideal). Crush the garlic and whisk together with the cream, milk, mustard and thyme leaves. Season generously.

3. 3

   Rub a large baking dish with a cut garlic clove. Layer half the potato slices in the dish, top with the caramelised onions and half the gruyère, then finish with the remaining potatoes.

4. 4

   Pour the cream mixture evenly over the top and scatter with the remaining gruyère.

5. 5

   Cover with foil and bake for 40 minutes, then remove the foil and bake for a further 20 minutes until the top is golden and the potatoes are completely tender when pierced.

6. 6

   Leave to stand for 10 minutes before serving alongside a watercress salad.