Melt the butter in a large saute pan over medium heat. Add the onions and saute until softened, about 3 minutes. Add the chicken stock, heavy cream, corn and some salt and pepper and cook, stirring occasionally, until the liquid is mostly evaporated and the corn is soft. If the corn isn¿t done but the liquid is gone, add a little more stock and continue cooking. Stir in the vinegar and serve.