In a medium-sized heavy pot (e.g., Dutch oven) fry the bacon until crispy. Remove half of the bacon fat. Add the onions and cook until golden brown, about 10 minutes. Add the remaining ingredients and bring to a boil. Reduce the heat to low and simmer, uncovered, for 35-45 minutes, stirring occasionally, until it's a rich brown and a spreadable consistency. Discard the thyme sprigs.