Trim the base of the brussels and cut in 1/2 lengthwise.
Heat a saute pan over high heat. Render the bacon until the fat has melted and it begins to caramelize. Then add the onion. Stir and cook until translucent with a little browning.
Add in the brussel sprouts and allow them to brown a bit before stirring. Cook about a minute. Add a little bit of water to steam the brussels. They should take on a bright green hue. Season and serve hot. You can add in a little butter if you want. But, with all the bacon fat, it shouldn't be necessary.