Cut the carrot into 1cm-thick batons. Trim the baby broccoli and halve widthwise (halve any larger pieces lengthwise). Peel the sweet potatoes, then cut into 2cm chunks. Finely chop the chives. Crumble 1 stock cube* into a jug, add 125ml (½ cup) milk and 125ml (½ cup) water and stir to dissolve.
Step 2 — Make meatballs
Bring a medium saucepan of water to the boil for the vegetables. Coarsely grate the onion into a large bowl. Add the breadcrumbs, beef mince, country seasoning, 2 tsp worcestershire sauce* and 1 tbs milk. Season with pepper. Using damp hands, combine well, then shape into walnut-sized meatballs.
Step 3 — Cook sweet potato
Put the sweet potato in a separate medium saucepan, cover with cold salted water and bring to the boil. Reduce the heat to medium and cook for 12-14 mins until tender. Turn off the heat, drain well and return to the pan. Cover to keep warm.
Step 4 — Brown meatballs
While the sweet potato is cooking, heat 2 tsp olive oil in a medium deep frypan over medium-high heat. Cook the meatballs, turning, for 3 mins or until browned (the meatballs won't be cooked through). Remove from the pan. Cook the carrot in the pan of boiling water for 3 mins. Add the baby broccoli and cook for a further 5 mins or until the vegetables are tender. Drain.
Step 5 — Make sauce
Meanwhile, melt 20g butter in the same pan over medium heat. Add 1 tbs flour and cook, stirring, for 1 min or until foaming. Gradually add the stock mixture, stirring constantly to prevent lumps from forming. Add the meatballs and bring to a simmer. Reduce heat to medium-low and cook, partially covered, for 5 mins or until meatballs are cooked through and the sauce is thickened.
Step 6 — Make mash and serve
Add 2 tsp extra virgin olive oil to the cooked sweet potato, season with salt and pepper and mash until smooth. Divide the mash, vegetables, meatballs and sauce among plates. Scatter with the chives to serve.