Meanwhile, make the sauce. Wrap the bacon around the middle of the thyme sprigs and tie with kitchen twine so you have a nice bundle. Heat a little oil in a large saucepan over medium heat. Add the thyme bundle and cook slowly for 3 to 4 minutes to render the bacon fat and give the sauce a nice smoky taste. Add the onion and garlic and cook slowly, without colouring, for 5 minutes. Add all of the rest of the sauce ingredients, give the sauce a stir, and turn the heat down to low. Cook slowly for 20 minutes to meld the flavours. Put some sauce in a separate bowl for basting, reserving the remaining sauce for serving.