Heat your oven to 200°C/Fan 180°C/Gas 6.
Scrub the sweet potatoes and chop into thick wedges. Scrub the carrots and halve them. Place the veg on a large baking tray. Drizzle with 1 tbsp oil and season with salt and pepper. Roast for 35 mins till tender and a little charred.
While the veg are cooking, unwrap the Brie. Place on a large square of foil. Peel and thinly slice the garlic. Using a sharp knife, make 8-10 small cuts in the Brie. Push a slice of garlic and a few rosemary leaves into each cut.
Grind over some black pepper. Bring the edges of the foil together and scrunch together to form a sealed parcel. Pop the parcel on a baking tray. Slide into the oven below the veg and bake for 30 mins.
Peel and thinly slice the onions. Heat a small frying pan for 1 min. Add ½ tbsp olive oil and the onions. Season with salt and pepper. Keep the heat low and gently cook the onions for 10 mins, stirring till soft. Pour in 1 tbsp balsamic vinegar and stir in any remaining rosemary leaves. Cook and stir for 2 mins. Take off the heat.
Trim the leaves off the radishes, leaving a little bit of stalk on each one so you can hold that when dunking them in the cheese. (See our tip for what to do with the leaves.)
Place the Brie parcel on a large plate and carefully unwrap the foil. The brie should be soft and oozey. Spoon the balsamic onions over the top. Serve the Brie with the roast veg and radishes for dunking, and the salad leaves on the side.