In a large bowl or stand mixer, beat softened butter until it is smooth and creamy, making sure to scrape the sides of the bowl. Add granulated sugar and packed brown sugar, and continue beating for about 2 minutes until the mixture is fluffy, scraping the sides to ensure there are no butter chunks remaining.

Next, add peanut butter and mix until well combined. Then add 1 egg and vanilla extract, beating the mixture until it is thoroughly combined, occasionally scraping the sides of the bowl.

Measure out 1 and 1/2 cups of all-purpose flour by spooning it into the measuring cup and leveling it off. Add the flour to the bowl without stirring it in just yet. On top of the flour, add baking soda, baking powder, and kosher salt. Use a teaspoon to stir these dry ingredients together slightly, ensuring any clumps are broken up.

Turn the mixer on to combine the dry ingredients with the dough, being careful not to overmix. Once the dough begins to come together and there is still some visible flour, stop the mixer and scrape down the sides and bottom of the bowl. Overmixing can result in tough cookies.

Cover the bowl and chill the dough for 15 minutes to an hour (or up to 24 hours).

Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper or a silicone baking mat. Shape the dough into 2-inch balls, using a cookie scoop and overpacking it slightly.

Place the dough balls on a baking sheet, ensuring they are at least an inch or two apart. You should be able to fit 12 cookies on a 12×18 inch half baking sheet.

Bake the cookies at 350 degrees F for about 10 minutes. They are done when the edges are set and the centers are no longer shiny. The cookies will be puffy but should have spread a bit. If they have not spread enough, gently press down on the tops of the cookies with a spatula either after removing them from the oven or 2 minutes before they are done baking. Top each cookie with additional Butterfinger crumbles if you have any left.

Allow the cookies to set on the pan for at least 5 minutes before transferring them to a wire rack to cool completely.

Note: These cookies are best enjoyed at room temperature rather than warm, as the melted Butterfinger can create a chewy texture that some may not prefer.

This recipe yields about 24 cookies. Store leftovers in an airtight container for up to 3 days. The dough can be frozen by placing cookie dough balls in a ziplock bag and freezing for up to 3 months. Bake the frozen dough balls as directed, adding an extra minute or two if necessary, and be prepared to press them down with a spatula after baking to help them spread.

Baked cookies can also be frozen in a sealed container for up to 4 weeks. Let them thaw at room temperature while still sealed.