Cream Butter and Sugars: In a large bowl or stand mixer, beat 3/4 cup softened butter until smooth and creamy, scraping the sides as needed. Add 1/2 cup granulated sugar and 1/2 cup packed brown sugar, and beat for about 2 minutes until the mixture is fluffy and well combined. Make sure there are no chunks of butter.
Add Peanut Butter and Wet Ingredients: Mix in 1 cup peanut butter until smooth. Then add 1 large egg and 1 1/2 teaspoons vanilla extract, beating until everything is fully incorporated. Scrape down the sides of the bowl as needed.
Combine Dry Ingredients: Add 1 1/2 cups all-purpose flour, 1/2 teaspoon baking soda, 1/2 teaspoon baking powder, and 1/4 teaspoon kosher salt to the bowl, but don’t mix yet. Stir the dry ingredients together lightly with a spoon or teaspoon to break up any clumps before turning on the mixer. Then, mix until just combined, being careful not to overmix.
Add Butterfingers: Gently fold in 16 ounces of chopped Butterfingers until just incorporated. You can use pre-packaged Butterfinger Bits or chop full-size Butterfinger bars if needed.
Chill the Dough: Cover the dough and chill for 15 minutes to an hour (or up to 24 hours) to firm up the dough and enhance the flavor. Try not to eat too much of the dough—it’s tempting!
Preheat Oven: Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats.
Shape Cookies: Shape the chilled dough into 2-inch balls using a cookie scoop. Place them on the prepared baking sheets about 1-2 inches apart.
Bake: Bake the cookies for about 10 minutes, until the edges are set and the tops are no longer shiny. The cookies will be puffy, but should spread slightly. If they haven’t spread enough, gently press the tops with a spatula to flatten them slightly. If you have extra Butterfinger crumbles, sprinkle them on top of the warm cookies.
Cool: Let the cookies set on the baking sheet for at least 5 minutes before transferring them to a wire rack to cool completely. Although tempting, these cookies are best enjoyed when they have cooled to room temperature, allowing the Butterfinger pieces to regain their crunchy texture.