Slice the brussels sprouts thinly with a knife or a mandolin. Set a straight side sauté pan over med high heat and add the pecans. Cook stirring continually, until the pecans darken in color 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 continually, until the color brightens and the sprouts are just tender, approximately 6 minutes. Serve warm.