Preheat the oven to 180°C.
Heat olive oil in an ovenproof frying pan and brown the seasoned lamb for 4 minutes.
Add rosemary, thyme, crushed garlic, and sweet potatoes to the pan.
Roast in the oven for 12 minutes until the lamb is cooked and potatoes are tender.
Remove lamb from the oven and allow it to rest before slicing.
Melt butter in a saucepan and fry onion and chopped garlic until translucent.
Add brandy and simmer the liquid until reduced.
Pour in red wine and reduce by half through simmering.
Add chopped thyme and vegetable stock, then cook for 4 minutes.
Stir in the double cream to finish the sauce.
Plate the sweet potatoes, top with lamb slices, pour over sauce, and garnish with roasted garlic.