Preheat Your Oven: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish with butter to prevent sticking.

Mix the Wet Ingredients: In a large mixing bowl, cream together the softened butter, granulated sugar, brown sugar, and 1/2 cup peanut butter using an electric mixer. Beat until light and fluffy. Add the egg and vanilla extract, mixing until well incorporated.

Prepare the Dry Ingredients: In a separate bowl, sift together the flour, baking soda, and salt. Stir in the oatmeal.

Combine Wet and Dry Mixtures: Gradually mix the dry ingredients into the wet ingredients, stirring until fully combined. The dough will be thick and slightly sticky.

Assemble the Bars: Spread the batter evenly into the prepared baking dish. Sprinkle the butterscotch chips over the top, pressing them lightly into the batter.

Bake to Perfection: Bake for 20-25 minutes, or until the edges are golden brown. Insert a toothpick into the center to check for doneness; it should come out clean or with a few moist crumbs.

Prepare the Glaze: While the bars are baking, whisk together powdered sugar, milk, and the remaining 1/4 cup peanut butter until smooth and creamy.

Finish with a Glaze: As soon as the bars come out of the oven, pour the glaze over the warm surface, spreading it evenly with a spatula.

Cool and Serve: Let the bars cool completely before slicing to ensure clean cuts and allow the glaze to set properly.