Prepare the Dough: In a large mixing bowl or stand mixer, begin by beating 3/4 cup of softened butter until creamy, about 1 minute. Next, add 1/2 cup of granulated sugar and 1/2 cup of packed brown sugar, beating until light and fluffy, about 2 minutes.

Mix in the Wet Ingredients: Incorporate 1 cup of peanut butter, 1 large egg, and 1 and 1/2 teaspoons of vanilla extract into the butter-sugar mixture, blending until well combined.

Combine Dry Ingredients: Gradually add 1 and 1/2 cups of all-purpose flour, 1/2 teaspoon of baking soda, 1/2 teaspoon of baking powder, and 1/4 teaspoon of kosher salt into the wet mixture. Mix on low speed until just combined.

Fold in the Butterfinger: Gently fold in the 16 ounces of chopped Butterfinger candy bars until evenly distributed throughout the dough.

Chill the Dough: Cover the bowl with plastic wrap and chill in the refrigerator for at least 15 minutes.

Preheat and Prepare the Baking Sheet: Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.

Form the Cookies: Scoop the dough into heaping tablespoons and roll them into 2-inch balls, arranging them on the prepared baking sheets.

Bake the Cookies: Bake for approximately 10 minutes, or until the edges are set and the centers look slightly underbaked.

Press and Cool the Cookies: If your cookies are puffed, gently press the tops with a spatula. Allow to cool on the pan for about 5 minutes before transferring to a wire rack.

Let Cookies Cool Completely: Transfer cookies to a wire rack to cool completely.