Shepherd's pie baked in a cast iron pan

Press the ground lamb into a wide thin disc in a dry, cold 12-inch cast iron pan; turn the heat to high so it renders its own fat.

Grate the onion and carrots so they bind the filling.

When the lamb browns on the bottom, stir in the vegetables, breaking up the meat.

Cook about five minutes to evaporate water; when it dries out reduce the heat to medium and cook until a brown layer forms on the pan.

Stir in tomato paste and flour and cook a couple of minutes until burning is imminent.

Deglaze with half a bottle of white wine, scraping the pan clean.

Add Worcestershire sauce, dried thyme and sage, garlic powder and mustard powder; no salt yet.

Add water or stock to cover, reduce to a simmer and cook until thick, at least an extra half hour; add demi-glace cubes.

Peel the potatoes, cut into chunks, cover with water, bring to a boil and simmer until falling apart.

Drain through a gap in the lid; add a stick of butter off the heat to melt.

Reduce the filling until quite thick; season with pepper, more garlic powder and salt to taste; take off the heat to cool and thicken.

Mash the potatoes with milk and a pinch of salt until looser than wanted; mix in the cheddar and two egg yolks; season.

At the last second stir chopped rosemary and the frozen peas into the filling; smooth it.

Drop the still-hot potato in spoonfuls over the filling and pull it toward the edges with a spatula; texture the top.

Bake in a preheated 400F / 200C oven about half an hour, until bubbly and puffy; broil at the end if more browning is wanted.

Scatter sliced chives; rest at least 20 minutes before serving.