Preheat oven to 350 degrees. Use parchment paper or a silpat mat to line a baking sheet.
Cream the butter, sugar and brown sugar in a stand mixer until light and fluffy (about 2-3 minutes). Scrape the sides of the bowl to make sure all ingredients are blended.
Add in the peanut butter and vanilla and beat until combined. Add eggs. Mix.
Add in flour, baking soda, and salt. Stir until all combined. Hand stir in 1 1/4 cups chopped Butterfinger candy bars.
Scoop out dough and roll into balls. Scoop out about 1 TBSPs of dough for smaller cookies (or 1/4 cup dough for BIG cookies). Place dough balls on prepared pan (12 cookies to a pan if smaller cookies).
Bake for about 11-12 minutes. Remove from oven. Immediately sprinkle each cookie with Butterfinger candy pieces. Cool cookies on cookie sheet for 10 minutes before removing to cooling rack. NOTE: If you decide to make the bigger cookies, you’ll need to bake them for 13-15 minutes.
Melt chocolate chips in the microwave. Pour melted chocolate into a sandwich bag and cut off corner. Drizzle melted chocolate over each cookie. You can also skip the sandwich bag part and just drizzle chocolate with a fork.