Preheat your oven to 350°F (175°C). Line an 8-inch square pan with aluminum foil and spray it with cooking spray; set aside.
In a mixing bowl or stand mixer, combine the creamy peanut butter, softened butter, granulated sugar, and brown sugar. Beat on medium-high speed for about 3 minutes until creamy. Tip: Make sure your butter is softened to room temperature for best results.
Add the egg and vanilla extract to the mixture. Beat on medium-high speed until the mixture is light and fluffy, about 3 more minutes.
Mix in the flour, oats, and optional salt on low speed until just combined, about 1 minute. Tip: Avoid overmixing to keep the bars tender.
Spread the batter into the prepared pan, smoothing the top with a spatula. Sprinkle the butterscotch chips evenly over the top.
Bake for approximately 25 minutes, until the edges are slightly firm and the center is just set. Check for doneness by inserting a toothpick in the center; it should come out clean or with a few moist crumbs, but no batter. Tip: Keep an eye on the bars towards the end of baking to prevent overcooking.
While the bars bake, prepare the frosting. In a mixing bowl, combine the peanut butter, confectioners’ sugar, and cream. Beat on medium-high speed until smooth and creamy, about 3 minutes.
Once the bars are out of the oven, immediately spread the frosting over the top. Allow the bars to cool completely in the pan before slicing and serving. Tip: The bars can be stored at room temperature in an airtight container for up to 5 days.
Notes
For a twist, try adding chopped nuts or chocolate chips to the bars before baking.