- STEP 1
Boil the potatoes in salted water for 20 mins or until tender, then drain.
- STEP 2
Heat the grill to high. Mash the potatoes until smooth, then beat in the crème fraîche and half the cheese. Season to taste, then spoon the hot mash into a medium baking dish and smooth the top.
- STEP 3
Mix together the rest of the cheese, the mustard and thyme leaves. Spread over the mash with a spatula or the back of a spoon. Grill until the cheese is melting and golden, then serve with the beef.