Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking dish by lining it with parchment paper and greasing it.

Cream together 1 cup of softened butter, ½ cup granulated sugar, and ½ cup light brown sugar until light and fluffy. Add 2 large eggs and 1 teaspoon vanilla extract; mix well. Gradually add 2 cups flour, ½ teaspoon salt, and 1 teaspoon baking soda; fold in ½ cup chopped Butterfinger pieces.

Spread the dough evenly into the baking dish and bake for approximately 25 minutes. The edges should be golden brown.

Allow the bars to cool in the pan for 20-30 minutes before frosting.

In a separate bowl, beat together ½ cup of butter and ½ cup peanut butter until smooth. Gradually mix in 1 cup powdered sugar and 1 tablespoon milk until fluffy.

Spread the peanut butter frosting evenly over the cooled cookie bars and sprinkle with remaining chopped Butterfinger pieces.

Refrigerate the frosted bars for about 30 minutes before cutting into 16 squares and serving.