Melt the butter in a frying pan and add a dash of olive oil. Put the garlic and rosemary (or thyme) in the pan and fry for a few minutes on a low heat to flavour the oil and butter. Using a slotted spoon, remove the herbs and garlic and set aside.
Season the lamb steaks with salt and pepper. Fry the lamb to brown it on both sides. Add the halves of garlic and allow them to colour slightly in the pan. Transfer everything to a roasting tin, along with the reserved herbs and sliced garlic.
Heat the wine in a small saucepan and then pour it over the lamb. Cover the tin with foil and place in the oven to cook for 45 minutes - 1 hour, or until the meat is meltingly tender.
Once cooked, remove the meat, cover and keep warm. Set the garlic halves aside too. If the liquid doesn’t look thick enough for a sauce, strain the wine and cooking juices into a saucepan, squeezing the juices from the rosemary and garlic skins.
Simmer the juices until thickened. To thicken the sauce even more, you can mix together equal quantities of flour and butter in a small bowl. Whisk this mixture into the sauce and cook until the taste of flour is removed. Add salt and pepper to taste.
Serve the lamb with the baked garlic, mashed potatoes and the sauce poured over.