Preheat oven to 350°F and line a rimmed sheet pan with aluminum foil.
Lightly grease the foil with butter and line the baking sheet with graham crackers, breaking them where necessary to make them fit.
Combine butter, brown sugar, pecans, and salt in a medium saucepan over medium heat. Bring to a boil and let cook 2 minutes, stirring constantly.
Remove from heat and stir in vanilla. Immediately pour hot mixture over graham crackers and spread mixture to edges of pan using a spatula. Make sure pecans are evenly distributed and that crackers are covered.
Bake until bubbly, about 10 minutes.
Allow to cool completely and break into pieces. Enjoy!