Preheat the oven to 350°F (175°C). Grease the baking pan.

In a mixing bowl, combine melted butter, brown sugar, flour, oats, baking soda, and vanilla extract. Mix until well combined.

Press the mixture evenly into the bottom of the prepared baking pan.

Bake for 10-12 minutes or until lightly golden. Remove from oven and let cool slightly.

In a saucepan over low heat, combine the unwrapped caramel candies and heavy cream. Stir until melted and smooth.

Pour the caramel mixture over the baked base and spread evenly.

Sprinkle the chopped Butterfinger bars evenly over the caramel layer.

Melt the milk chocolate chips in the microwave or over a double boiler, then drizzle over the Butterfinger layer.

Let cool completely before cutting into bars.