Cook the carrots in boiling water for 10-15 minutes until they are starting to soften, but still have some bite. Drain and pat dry.
Spread the carrots out in a roasting tin. Drizzle with the oil and vinegar, then sprinkle with sugar. Season well with sea salt and black pepper, then roast for about 45 minutes, turning occasionally until the sugar has caramelised and the carrots are soft and tender.