Preparation

1. Heat the beer to reduce it to 120 ml, add the vinegar and olive oil and simmer for a few minutes.
2. Meanwhile, quickly sear the mackerel filets in a small amount of oil.
3. Place them in a dish and cover with the onion, celery, garlic, shallot, carrots, bay leaves and thyme; salt and pepper to taste.
4. Bring the beer mixture to a boil, stir in the mustard, and pour over the fish.
5. Marinate in the fridge for 24 hours.
6. The next day, cook the potatoes in their skins in salted boiling water.
7. Meanwhile, make the roquette pesto by mixing all the ingredients in a blender.
8. Dice or slice the cooked potatoes and coat them with the pesto.
9. Serve with the marinated mackerel.
10. Garnish the plates with roquette leaves if you wish.