Preheat the oven to 220C, fan-forced. Line an oven tray with baking paper. Remove 20g butter from the fridge to soften. Combine the maple syrup, 2 tsp olive oil, 2 tsp balsamic vinegar and 2 tsp dijon mustard in a large bowl and season with salt and pepper. Add the lamb and turn to coat.
Step 2 — Prep ingredients
Halve the unpeeled potatoes, quartering any large ones. Cut the carrot into 1.5cm-thick batons. Trim the beans and halve on an angle. Crush or finely chop the garlic. Pick the rosemary leaves, discarding the stems.
Step 3 — Roast vegetables
Put the garlic, rosemary and softened butter in a large bowl and season with salt and pepper. Mash with a fork to combine. Add the potatoes, carrot and beans and toss to coat. Transfer the vegetables to the lined tray. Roast on the lower oven shelf for 20-25 mins until golden and tender.
Step 4 — Brown and roast lamb
Meanwhile, heat a small flameproof roasting pan over high heat (see cooking tip). Cook the lamb, turning regularly, for 2 mins or until browned. Transfer the pan to the upper shelf of the oven. Roast the lamb for 5-6 mins for medium-rare, or until cooked to your liking. Remove the lamb from the oven and rest for 8 mins.
Step 5 — Make dressing
While the lamb is roasting, finely grate the zest of half the lemon*, then juice the half. Finely chop the parsley leaves, discarding the stems. Combine the lemon zest, parsley, 1 tbs lemon juice and 2 tsp extra virgin olive oil in a bowl. Stir in the crumbled feta.
Step 6 — Slice lamb and serve
Slice the lamb. Divide the lamb and vegetables among plates. Spoon the dressing over the vegetables. Drizzle any pan juices and resting juices over the lamb to serve, if desired.