2. Meanwhile, place the bacon in a large pot over medium-high heat. Sauté for 2 minutes, stirring. Turn heat down to medium and add the garlic. Sauté for 1 minute, stirring. Over sink, squeeze the tomatoes in your hands into a strainer until most of the juice has run out. Chop the tomatoes and add to the pot. Add the chipotles in adobo sauce, making sure the chipotles are cut into small pieces (some cans may contain whole chipotles, some may contain chopped chipotles). Add the barbecue sauce, the reserved mushrooms, and the reserved soaking liquid. Bring to a boil, then lower heat and simmer for 10 minutes.
3. When ready to serve, turn heat off and whisk in the butter to velvetize the sauce.
Adam Rapoport, editor in chief of Bon Appetit magazine and the website www.bonappetit.com, knows his way around a grill. He has edited an entire book on the subject: The Grilling Book: The Definitive Guide from Bon Appetit.