Preheat your oven to 160°C (140°C fan/Gas 3).

In a hot, ovenproof frying pan or flameproof casserole, heat sunflower oil over medium-high heat. Add the lamb neck fillet in batches, frying until deep golden brown, about 4-5 minutes per side. Remove and set aside.

In the same pan, add sliced leeks and red pepper, sautéing for 3-4 minutes until softened. Stir frequently to prevent sticking.

Incorporate grated garlic, cayenne pepper, and ground cumin into the sautéed vegetables, frying briefly for about 10 seconds.

Stir in the passata and a splash of water, bringing to a gentle boil. Scrape up any browned bits from the bottom of the pan. Return the browned lamb to the pan.

Season generously with salt and pepper. Cover the pan and transfer to the preheated oven. Cook for 2 hours.

After 2 hours, remove the stew from the oven and let steam escape. Stir in balsamic glaze and baby spinach leaves until wilted.

Taste and adjust seasoning as needed. Serve hot over rice or mashed potatoes.