- Preheat oven to 160 degrees C (Gas Mark 3).
- In shallow roasting pan, place lamb, fat side up.
- With sharp knife, cut slits in lamb.
- Insert garlic slivers in slits.
- Roast lamb for 1.5-2 hours until cooked to your preference.
- Allow lamb to stand in a warm place for 15 to 20 minutes before carving.
- Meanwhile, in medium saucepan, combine remaining ingredients.
- Simmer, stirring constantly, until thickened.
Serve with mash / roast potatoes and veg.