To make blueberry barbecue sauce, place the first 8 ingredients in a medium pot. Gently simmer over medium heat 10 minutes. Puree mixture in a food processor or in the pot with an immersion blender. Return to a simmer; mix in the cornstarch mixture. Simmer until the sauce has lightly thickened, about 2 minutes, then remove from heat.
Preheat your barbecue to medium-high. Grill the bison patties three to four minutes per side, or until cooked through. Spread each patty with sauce and heat through 1 minute.
Sandwich the patties in the buns with the mayonnaise, lettuce, onions and bacon, and serve.
Note: This recipe yields about 3 cups of blueberry barbecue sauce, more than you’ll need for the burgers. Keep the leftover sauce in a tightly sealed jar in the refrigerator for another time. It will keep at least week. Beyond burgers, you can also slather it on barbecued chicken, pork ribs and chops, and salmon.