Preheat the oven to 200C, fan-forced. Line 2 oven trays with baking paper. Peel and cut the sweet potatoes into 3cm chunks. Quarter the carrot lengthwise, then cut in half. Coarsely chop the broccoli stem, then cut the head into small florets. Crumble 1 stock cube* into a heatproof jug, add 125ml (½ cup) boiling water and stir to dissolve.
Step 2 — Roast lamb
Drizzle the lamb with 2 tsp olive oil and season with salt and pepper. Heat a medium frypan over high heat until hot. Cook the lamb, turning regularly, for 4 mins or until browned. Transfer to a lined tray, reserving the pan. Roast the lamb on the upper oven shelf for 12-15 mins for medium-rare, or until cooked to your liking. Remove from the oven and rest for 8 mins.
Step 3 — Roast veggies
Meanwhile, put the carrot and broccoli stem on the remaining lined tray, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Roast on lower shelf for 15 mins. Put broccoli florets in a bowl, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Add to the carrot and roast for a further 10 mins or until veggies are tender.
Step 4 — Make sweet potato mash
While the lamb is roasting, put the sweet potato in a medium saucepan of cold salted water and bring to the boil. Reduce the heat to medium and cook for 12-15 mins until tender. Drain and return to the pan. Mash the sweet potato until smooth. Add 10g butter, season with salt and pepper and stir to combine.
Step 5 — Make beetroot gravy
Melt 10g butter in the reserved pan over medium heat. Add 2 tsp plain flour and cook, stirring, for 2 mins or until foaming. Gradually add the stock, stirring constantly, and bring to the boil. Reduce the heat to medium and cook, stirring, for 2 mins or until thickened. Stir in the beetroot relish. Remove from the heat. Taste, then season with salt and pepper.
Step 6 — Serve up
Thinly slice the lamb. Divide the lamb, sweet potato mash and roast veggies among plates. Drizzle over the beetroot gravy and enjoy!