Preheat your oven to 350°F (175°C).
Prepare a baking dish by greasing it or lining it with parchment paper.
In a bowl, mix together the graham cracker crumbs, melted butter, and sugar until well combined.
Press the graham cracker mixture into the bottom of the prepared baking dish.
In a saucepan over low heat, combine the butter, granulated sugar, brown sugar, condensed milk, and peanut butter, stirring until smooth.
Once the mixture is smooth, add in the Butterfinger pieces and vanilla extract, mixing until evenly distributed.
Pour the filling over the crust in the baking dish and spread it evenly.
Bake in the preheated oven for 25-30 minutes until the filling is bubbly and the edges are golden brown.
Remove from the oven and allow the bars to cool completely in the pan before slicing.
Once cooled, lift the bars out of the pan using the parchment paper and cut into squares for serving.
