Chorizo and potato salad
First, make the dressing. Mix together the walnut oil, the extra-virgin olive oil, the sherry vinegar, the wholegrain mustard, the crushed garlic, and some sea salt and freshly ground black pepper.
Put a large pan of salted water on a high heat and bring it to the boil. When it is boiling, add the cubes of potato and cook them for three minutes. Drain and set aside. Put a frying pan on a medium heat and allow it to get quite warm. Tip the chorizo into the pan with a tiny drizzle of extra-virgin olive oil and cook it for a couple of minutes, tossing once or twice, until the chorizo releases its oils. Spoon out the chorizo and set aside, leaving any oil in the pan. Turn the heat up to high. Add the potatoes to the pan and cook them, tossing them regularly, until they are cooked and golden.
Tip the chorizo back into the pan along with 2 tablespoons of the dressing and toss everything for a few seconds until the dressing has soaked into the chorizo and the potatoes. Turn off the heat and set the pan aside.
Put the leaves in a bowl and season them lightly with a pinch of sea salt and freshly ground black pepper. Drizzle some of the dressing over the leaves, and toss gently with your hands until the leaves are just glistening. You may not need all the dressing. Put the dressed leaves on plates, or on one large plate, then arrange the chorizo and the potatoes around them. Garnish with the grated Parmesan. Serve straight away.