First, preheat the oven to 160°C/gas mark 3

Boil some water in a saucepan on the hob and plunge the chopped watercress in for just a minute, or until the water comes back to the boil. Drain and leave to cool

Meanwhile, add a splash of olive oil to a frying pan and place on the hob over a medium heat. Add the leeks and slowly cook down until they become soft and sweet

Place the milk in a large bowl and add about 700g of the potato slices, along with the watercress. Mix together

Take a rectangular baking dish and very lightly oil the bottom and sides. Evenly add the slices of potato, layering up as you go through. When you are roughly halfway through, add a layer of the leeks and then continue until you have used them all up

Pour over any remaining milk, then with the remaining ‘clean’ potatoes, add a final layer. Press everything down and place in the oven for 50 minutes, until the top starts to crisp up

After that time, add the sprinkling of Gruyère and bake for a further 10 minutes, until it’s bubbled up and browned a touch

You can do this all in advance if you like, with the benefit of cooling down, covering with foil and pressing overnight in the fridge by placing a tray with some tins on top. This helps to compress the dauphinoise. Just reheat for 25 minutes or so before serving

To make the accompanying salmon, place all of your aromatics in a wide saucepan and fill with about a litre of water. Bring gently to a simmer and leave to cook for 10 minutes. Then place in the salmon and lightly poach them for 5 to 6 minutes, until they are just done. Lift out and keep in warm in foil while you make the sauce

Finish by pouring the remaining cooking liquor into a saucepan through a sieve to catch the aromatics. Quickly reduce on the hob by half then add the créme fraiche and stir through. The sauce will be quite light

Plate up with a slice of the dauphinoise, a fillet of salmon sat jauntily to the side, a drizzle of sauce and some pea shoots for colour