Trim the pork cheeks of excess fat and silver skin. Season with salt and freshly ground black pepper, then dust with plain flour, shaking off any excess.
Heat the extra-virgin olive oil in a large, heavy-based pan over a medium-high heat. Add the pork cheeks and brown on all sides until well caramelised. Remove and set aside.
In the same pan, add the finely chopped onion, chopped carrots and leek. Cook over a medium heat for 10-15 minutes, until the vegetables are soft and golden.
Add the sliced garlic and cook for another 2 minutes, until fragrant.
Pour in the red wine and bring to the boil. Cook for 2-3 minutes, scraping up any caramelised bits from the base of the pan.
Stir in the beef stock, bay leaves and sprig of thyme. Return the pork cheeks to the pan, ensuring they are submerged in the liquid.
If using a pressure cooker, cook on high pressure for 45-50 minutes once it has reached pressure, then allow the pressure to release naturally. If cooking in a regular pan, cover and simmer gently for 2½-3 hours, until the pork cheeks are tender.
Remove the pork cheeks from the pan and discard the bay leaves and thyme sprig. Purée the cooked vegetables in the pan with a hand blender until smooth. If the sauce is too thin, simmer for a few minutes to reduce, then season to taste with salt and pepper.
Return the pork cheeks to the sauce to warm through and soak up the flavours. Serve with mashed potato, chips or plain white rice.