Instructions
Follow the steps and taste along the way.
Prepare the leek and potatoes
Preheat the oven to 190 °C. Cut the leek into thin rings and the potatoes into even slices about 3 mm thick. Heat the olive oil in a pan, add the leek, and cook over medium heat for 6–8 minutes, until softened and lightly golden in places.
Warm the mustard cream
Finely chop the garlic and add it to the leek for the last minute of cooking. In a saucepan, mix the cream, milk, Dijon mustard, thyme, nutmeg, 6 g salt, and black pepper. Heat the mixture until hot and steaming, but do not let it boil.
Layer the gratin
Arrange half of the potatoes in a baking dish with a capacity of about 2 litres, top with half of the leek, and pour over some of the hot cream mixture. Repeat the layers and pour the remaining mixture evenly over the top. Cover the dish with foil and bake for 40 minutes at 190 °C.
Finish baking with the cheese crust
Mix the grated cheese with the breadcrumbs. Carefully remove the foil, sprinkle the cheese mixture evenly over the top, and bake uncovered for a further 25–30 minutes. The gratin is ready when the top is golden brown and a knife passes easily through the potatoes in the center. Let it rest for 8 minutes.
Finish the salad and serve
Toss the arugula with the lemon juice, 1 g salt, and a spoonful of warm liquid from the edge of the gratin. Divide the gratin into four portions and serve hot with the arugula, so the tangy dressing balances the creamy flavor.
