Clean the onions, wash them in cold water, drain well and dry with a tea towel. In a shallow stainless steel pan, brown the whole onions in the oil. Add the sugar over a low heat and, stirring constantly, let it caramelise and turn golden. At this point, pour the 2 tablespoons of vinegar over the onions, turn up the heat and let it evaporate. Pour in the boiling broth until the onions are almost completely covered, season with salt (and a little pepper, if you like) and let the onions simmer, with the lid on the pan, until they’re soft and well cooked. If they should dry out too much, add some more broth. When they’re ready, almost all the liquid should have been absorbed. Serve the onions nice and hot as a side dish with roast, grilled or fried meat, or with stews. They can also be served as an appetizer, or on thick slices of toasted bread as a vegetarian main course.