Preheat the oven to 200°C and bring the lamb to room temperature.
Mix finely grated garlic with softened butter in a bowl.
Add finely chopped rosemary, salt, and pepper to the butter and mash into a paste.
Make 30 to 50 small incisions into the lamb flesh using a knife or skewer.
Massage the garlic butter mixture into the meat and the created holes.
Place lamb in a roasting tin, cover with foil, and roast in the oven.
Remove the foil after 30 minutes and roast for another 50-60 minutes.
Remove lamb from oven and rest covered in foil for 10-15 minutes.
Heat pan juices with red wine in a frying pan and reduce the liquid.
Whisk in a paste of flour and butter to thicken the gravy to your liking.
Slice the lamb and serve with the gravy and fresh rosemary garnish.