2) In the meantime, preheat a large skillet and cook the back bacon for 2 minutes on each side. Remove the bacon from the pan, chop, and set aside. Add the oil and onion to the pan and cook until onions have softened, about 2 minutes. Add the collard greens and stir in the vinegar, maple syrup, red pepper flakes, and broth. Bring to a simmer and cook, covered, for 30 minutes. Add the chopped bacon to the pan, and season with salt.