Carefully break the graham crackers at the seams. To a quarter sheet pan, evenly distribute 51 graham crackers in a single layer.
Sprinkle chopped pecans in an even layer on top.
To a medium saucepan on medium heat, combine butter, sugar, and vanilla.
Once the butter has melted and combined with the sugar, turn the heat to medium-high and bring to a full boil. Allow the mixture to boil for EXACTLY 2 minutes, stirring occasionally and very carefully to avoid splashing!
Slowly and carefully pour the butter mixture over the graham crackers. Spread the mixture with a rubber spatula, ensuring all pieces are covered and still evenly distributed. Bake in a preheated 350°F oven for 7-9 minutes or until the toffee coating is bubbling and crackers slightly browned.
Remove from the oven, allow them to rest 1 minute, then transfer one-by-one to a cooling rack or parchment paper using a small spatula and knife. Store in an air-tight container.