Heat a large Dutch oven over medium-high heat. Add the bacon and cook until crisp, about 5 minutes. Add the onions along with a pinch of salt and cook until the onions are translucent, 3 to 5 minutes. Add the beer, vinegar and another large pinch of salt. Cover and cook until the cabbage is wilted but is still slightly crisp. Stir in the mustard and taste for seasoning. You might want to add some additional salt, mustard and/or vinegar at this time.
Remove the cabbage from the heat and stir in the chives and parsley.