1. Preheat the oven to 400°F. Melt the butter on medium in an iron skillet. Add the bacon and let it render for a few minutes. Turn the heat up to high and dump in the sprouts. Cook for a minute or two, until slightly browned.
2. Pour in enough balsamic vinegar to come 1/4 of way up the brussels sprouts. It is a lot of vinegar. Cover the pan with foil, and transfer to the oven. Cook for 15 minutes.
3. Remove the foil, and return the pan to the burner over high heat. Cook until the balsamic vinegar reduces, about another minute. Season with salt and serve.
Variation: Add a dollop of cram to the pan and toss to coat sprouts.
