Preheat a pan with butter and olive oil over medium- low heat. Add in the onions and allow to cook slowly, stirring every so often until they soften, turn translucent and begin to caramelize in colour- about 45 minutes.

Once they begin to look caramelized, add in the brown sugar and balsamic and season with salt and pepper to taste. Set aside.

Working in 3 batches, preheat a large nonstick skillet over medium high heat and add in 1 tbsp each of butter and olive oil. Add in 1/2 of the Brussels sprouts and pan-fry until dark brown on all sides. Season with salt and pepper, to taste. Transfer to a platter or bowl. Continue with another tablespoon each of butter and oil, and the other half of the Brussels sprouts. Then do the same with the quince. At this point, this can all be refrigerated until before time to serve or you can continue to step 2.

Heat the last tablespoon of oil in the skillet and add in the cooked Brussels Sprouts, quince, bacon jam and maple syrup. Toss until warmed through and well coated. Serve immediately.