Put the olive oil in a small frying pan over a low heat. Cook the shallots for 20 minutes until soft. Stir in the vinegar and sugar and cook for 5 minutes, until browned.
Meanwhile, heat a large pan of salted water until boiling. Add the Brussels sprouts and cook for 8-10 minutes until al dente.
Drain, place in a serving dish, scatter over the shallots and serve.
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