For the pigs' cheeks, preheat the oven to 150C/130C Fan/Gas 2.
Heat the oil in an ovenproof casserole over a medium heat. Add the pigs' cheeks and fry for 1-2 minutes on all sides, or until browned all over. Remove from the casserole and set aside.
Add the onion, carrots and garlic to the casserole and fry for 4-5 minutes, or until light golden-brown.
Add the cumin, smoked paprika and raisins, stir well and continue to cook for a further 1-2 minutes.
Pour in the sherry and bring to the boil, scraping up any burned bits from the bottom of the pan using a wooden spoon. Continue to boil until the volume of sherry has reduced by two-thirds.
Return the pigs' cheeks to the casserole, the pour over the stock and return the mixture to the boil. Transfer the casserole to the oven and cook for 2-2½ hours, or until the pigs' cheeks are tender and the cooking liquid has reduced and thickened to a sauce.
Meanwhile, for the garlic-cumin potatoes, boil the potato cubes in a pan of salted water for 8-10 minutes, or until tender. Drain well, mash using a potato ricer or masher, then set aside to cool.
Heat the oil in a frying pan over a medium heat. Add the garlic and cumin and fry until the garlic is pale golden-brown.
Mix together the mashed potatoes, garlic, cumin and the cooking oil in a bowl until well combined. Stir in the butter, then season, to taste, with salt and freshly ground black pepper. Keep warm.
For the picada, blend all of the picada ingredients to a thick paste in a food processor. Season, to taste, with salt and freshly ground black pepper.
When the pigs' cheeks are cooked, remove the casserole from the oven and place it on the hob over a medium heat. Stir in the chocolate and the three-quarters of the picada and simmer for 2-3 minutes, or until the chocolate has melted and the sauce has thickened a little more. Season, to taste, with salt and freshly ground black pepper.
To serve, divide the pigs' cheeks equally among 4 serving bowls. Spoon the potatoes alongside. Garnish each dish with some of the remaining picada.