Line a jelly roll sheet with foil and place the graham crackers tightly all across it.
Preheat oven to 350.
Bring the butter and sugar to boil in a large saucepan over medium heat for 5 minutes while stirring. Add in the pecans and vanilla and cook for 2 minutes.
Pour the hot mixture over the graham crackers evenly.
Bake immediately for 10 minutes.
Allow to cool before breaking into pieces and storing the bark.