Potato, tuna and spinach gratin

Turn the oven on to 180 °C (thermostat 6), regular bake. Take the frozen spinach out of the freezer and put it in a colander to thaw while you prep the rest.

Peel the potatoes (0.7 kg) and cut them into 3 mm rounds. Put them in a saucepan of cold salted water, bring to a boil, then cook 8 min, they should stay a little firm. Drain.

Slice the onion. Melt 10 g of butter in the skillet over medium heat and sauté the onion for 5 min until translucent.

Squeeze the spinach by hand in the colander to get all the water out, then roughly chop it with the knife.

Add the spinach to the skillet with the onion and heat it for 5 min over medium heat, stirring. Salt, pepper and add the pinch of nutmeg.

Drain the tuna and flake it into the mixing bowl. Add the spinach with the onion and the crème fraîche (13 cl), then mix. Butter the baking dish with the remaining 10 g of butter.

Spread half the potatoes in the dish, cover with the tuna and spinach mix, then finish with the rest of the potatoes. Spread half the Gruyère (50 g) on top.

Bake the dish at 180 °C (thermostat 6) for 15 min.

Add the rest of the Gruyère (50 g), then switch the oven to broil. Finish 2 to 3 min under the broiler until the top is golden.