Slice the Brussels sprouts using the thinnest slicing disc of a food processor. A mandoline or knife would also work.
Set a 10-inch straight-sided saute pan over medium-high heat and add the pecans. Cook, stirring continually, until the pecans darken and begin to give off a toasted aroma, approximately 2 minutes.
Add the butter to the pan and stir to combine. Once the butter has melted, add the Brussels sprouts, salt, and pepper, and cook, stirring continuously, until the color brightens and the sprouts are just tender, approximately 6 minutes.
Remove the pan from the heat, add the cranberries, toss, and serve. Yes, it's really that simple.