Preheat your oven to 350°F (175°C).
In a heatproof bowl, combine the unsalted butter and bittersweet chocolate chips. Melt them together using a microwave in 30-second intervals, stirring in between, until smooth and fully combined.
Once the chocolate and butter mixture is melted and slightly cooled, whisk in the granulated sugar, salt, and vanilla extract until well combined.
Add the eggs one at a time, stirring well after each addition.
In a separate bowl, whisk together the all-purpose flour and baking soda. Gradually fold this mixture into the wet ingredients until just combined.
Gently fold in the chopped Butterfinger candy bars, making sure they are evenly distributed throughout the cookie dough.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto a parchment-lined baking sheet, spacing them about 2 inches apart. Bake in the preheated oven for 10-12 minutes.
Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.
