Finely dice the onion and garlic. Cook both in a sauce pan with vegetable oil over medium heat until softened (3-5 minutes). Meanwhile, roughly chop one chipotle pepper and reserve 1 Tbsp of adobo sauce from the can.
Add the tomato sauce, raspberry jam, cider vinegar, chopped chipotle pepper and adobo sauce to the cooked onions and garlic. Stir everything well and bring up to a simmer. Continue to simmer for about 45 minutes, stirring occasionally. Allow the sauce to cool after simmering (it will thicken upon cooling).
Remove the skin from the chicken and trim any excess fat. The skin should pull away from the meat easily although you may need a small sharp knife to separate it in some places. Preheat the oven to 375 degrees.
Prepare a baking sheet with aluminum foil and non-stick spray. Place the chicken thighs on the tray and slather with BBQ sauce (pour a small amount of sauce into a bowl before brushing onto chicken so that the whole batch will not get contaminated with raw chicken).
Place the BBQ chicken in the oven and bake for 45 minutes. Fifteen and thirty minutes into the cooking time, take the chicken out and slather with more sauce.