Preheat the oven to 350 degrees F. Line a baking sheet with a Silpat or parchment.
In a small bowl, whisk together the brown sugar, salt, cayenne (if using), salt, pepper, and melted butter. Stir together the chopped rosemary and the pecans in a separate bowl. Pour the butter blend over the pecans and toss to combine until everything is coated.
Pour out the pecans onto the prepared baking sheet, making sure to spread them out. Bake for about 10 minutes, or until toasted.