If using bacon, only use 1 tablespoon of butter and oil.
Add the butter and olive oil to a large skillet over medium heat. If you are using bacon, add it now and let it cook for 1-2 minutes.
Crush the garlic against a cutting board with the bottom of a can or jar.
Once the butter has melted, add the garlic.
Sauté the garlic on medium for a few minutes until just golden. Break the garlic apart more with a wooden spoon.
Remove the garlic and bacon with a slotted spoon. Reserve for later.
Increase the heat to medium high, add the greens and stir. Then stop stirring! You want the greens to make contact with the pan so they can develop color.
Add the salt, pepper and red pepper flakes, if using. Cook the greens without stirring for 5-8 minutes or until the bottom is somewhat browned, almost charred in places.
Reduce the heat to medium low. Add back in the garlic and bacon (if using).
Add the vinegar and cook for about 5 minutes for the flavors to combine and the greens to soften a bit. If you prefer the greens softer, cook for longer on a lower heat. The vinegar will mellow and add a brightness to the greens. Taste the greens and see if you need additional salt or vinegar.