In a cast-iron skillet, melt the butter over medium heat. Add in the brown sugar and stir until well combined.
Add the pecans and stir to completely coat them in the butter. Cook, stirring frequently, until toasted, about 8 minutes.
Scrape onto a sheet of wax paper and let cool to room temperature. Break apart as necessary before using.
Store in an airtight container at room temperature for up to 4 days.