1/2 cup (1 stick) butter, at room temperature, plus more for greasing pan
1/2 cup granulated sugar
1/2 cup light brown sugar, packed
3/4 cup creamy peanut butter, divided
1 large egg
1 teaspoon vanilla extract
1 cup all-purpose flour
1 teaspoon baking soda
1/4 teaspoon salt
1/2 cup quick-cooking oatmeal
1 cup butterscotch chips
1 cup powdered sugar
4 tablespoons milk
Preheat oven to 350°F and grease a 9×13-inch baking dish with butter.
In a large bowl, cream together the butter, granulated sugar, brown sugar, and 1/2 cup of the peanut butter with an electric mixer.
Add egg and vanilla and mix to combine.
Sift together flour, baking soda, and salt. Add oatmeal and stir to combine.
Add flour/oat mixture to butter mixture and mix on low until well combined.
Spread evenly across prepared baking pan and top with butterscotch chips.
Bake until golden brown on the edges, 20-25 minutes.
Whisk together powdered sugar, milk, and remaining 1/4 cup peanut butter until smooth, then pour evenly over bars while still warm.
Let cool completely before slicing and serving. Enjoy!