Melt butter in a saucepan over medium heat. Cook and stir brown sugar in hot butter until dissolved. Add cinnamon and stir until fragrant, about 1 minute.
Stir vanilla into brown sugar mixture; cook and stir until vanilla stops sizzling, about 30 seconds. Add pecans; cook and stir until pecans are fragrant and lightly toasted, about 1 minute. Pour pecan mixture out in a layer on parchment paper. Let cool to room temperature before breaking into pieces, about 20 minutes.
