Place the sweet potato and potato in a large pot, cover with cold, salted water and bring to a boil. Cook until tender and easily pierced with a fork, about 15–20 minutes.

Drain in a colander then return to the pot or a bowl. Add the milk, a pinch of salt, and pepper, and mash until smooth and creamy. The mix of floury potato and sweet potato gives a beautifully balanced mash — not too sweet, with a fluffy texture.

Set the mash aside. If making ahead, press a sheet of plastic wrap directly onto the surface of the mash to prevent a skin forming, and refrigerate for up to 2 days.

Heat a large, deep, oven-safe pot over medium-high heat. Add the lamb mince and cook, breaking it up with a spoon, until browned all over and any liquid has fully evaporated. Don't rush this step — a good sear on the mince builds depth of flavour.

Reduce heat to medium. Stir in the onion, carrot, celery and garlic. Cook for 5–7 minutes, stirring occasionally, until the vegetables are softened and fragrant.

Add the cumin, paprika, salt, and pepper. Stir well to coat the meat and veg in the spices and cook for 1 minute until aromatic.

Push the meat and vegetables to one side of the pan. Add the tomato paste to the cleared space and cook, stirring, for about 1 minute until it darkens slightly and becomes fragrant. Then mix it into the rest of the filling.

Strip the rosemary and thyme leaves from their woody stems and add the leaves to the pan. Stir through.

Pour in the beef stock, bring to a simmer, and cook uncovered for 20–25 minutes, stirring occasionally, until the filling has thickened and most of the liquid has reduced.

Stir in the frozen peas and cook for another 2–3 minutes until heated through. Taste and adjust seasoning. Remove from heat.

Preheat your oven to 200°C (180°C fan-forced).

If the mash has been refrigerated, give it a quick stir. If it feels too thick, fold in a small splash of warm milk to loosen it slightly.

Spread the mash evenly over the lamb filling directly in the same pot, working from the edges inward to create a good seal.

Using a fork, gently drag it across the surface of the mash to create small ridges. These textured peaks will crisp up and turn golden in the oven.

Place in the oven and bake for 20–25 minutes, or until the top is lightly golden and the filling is bubbling around the edges. If baking from cold (straight from the fridge), add an extra 10–15 minutes and cover loosely with foil for the first 15 minutes, then uncover to brown the top.

Remove from the oven and rest for 5 minutes before serving.

Sprinkle with freshly chopped chives and serve hot with a side of greens or a simple salad.

To make ahead: Prepare the lamb filling and mash topping separately. Cool both completely before storing in airtight containers in the fridge for up to 2 days.

To assemble ahead: Spread the mash over the cooled filling in the oven-safe pot, cover tightly with foil or a lid, and refrigerate for up to 2 days. When ready to bake, remove from the fridge