For the crust:

1. Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking pan or line it with parchment paper for easy removal.
2. In a medium bowl, combine the flour, melted butter, granulated sugar, and salt. Mix until the dough forms a crumbly texture.
3. Press the mixture evenly into the bottom of the prepared pan to form the crust.
4. Bake for 10-12 minutes, or until the crust is lightly golden. Remove from the oven and let it cool slightly while you prepare the caramel layer.

For the caramel layer:

1. In a medium saucepan over medium heat, melt the butter.
2. Stir in the brown sugar, sweetened condensed milk, vanilla extract, and salt. Bring the mixture to a simmer while stirring constantly.
3. Let the caramel cook for 3-5 minutes, or until it thickens slightly. Remove from heat.
4. Pour the caramel evenly over the cooled crust, spreading it to cover the entire surface.

For the topping:

1. Sprinkle the crushed Butterfinger pieces evenly over the caramel layer, pressing them down gently.
2. In a small saucepan, melt the chocolate chips and butter together over low heat, stirring until smooth and glossy.
3. Pour the melted chocolate over the Butterfinger and caramel layers, spreading it evenly to cover.
4. Let the bars cool completely at room temperature, or refrigerate for about 30-60 minutes to speed up the setting process.

To serve:

1. Once the chocolate has hardened, cut the bars into squares. Serve and enjoy!