Preheat the oven to 350 degrees. Line a rimmed baking sheet with parchment paper. Line the sheet with the graham crackers – you may have a few leftovers depending on how large your baking sheet is.
Melt the butter in a medium saucepan over medium heat. Add the brown sugar and stir well to combine. Continue to cook until the mixture starts to bubble. Once it starts to bubble, continue cooking, stirring constantly, for 2 minutes. Remove from the heat and stir in the vanilla and pecans. Carefully pour the mixture over the graham crackers, spreading in an even layer. Bake for 10-12 minutes.
Remove from the oven and sprinkle with the sea salt. While still warm, cut into bite-sized pieces. Let cool.