Prep: Line a baking sheet with parchment paper.
Warm the syrup: In a cast iron skillet over medium heat, simmer the maple syrup for about 15 seconds.
Add sugar and spice: Stir in the first ½ cup brown sugar and the cinnamon.
Add bourbon and vanilla: Carefully pour in the bourbon and vanilla. Simmer for about 30 seconds, stirring constantly.
Add pecans: Add the pecans and stir until well coated.
Cook down: Simmer and stir until the glaze is thick, sticks to the spatula, and almost no liquid is left.
Rest: Turn off the heat and let sit for 1 minute, then stir again.
Coat: Add the second ½ cup brown sugar and stir until the pecans are well coated.
Toss: Transfer to a glass bowl and mix again.
Cool: Spread the pecans on the baking sheet in a single layer and let cool completely until dry and crunchy.