Preheat your oven to 350 degrees Fahrenheit. Line a 9X13-inch baking dish with aluminum foil and lightly coat the foil with cooking spray. This will ensure that your bars release easily after baking.
In a large mixing bowl, combine the melted butter, brown sugar, baking soda, and salt. Using a hand-held mixer, blend these ingredients until smooth and creamy. The mixture should be thick and well combined, with no lumps.
Add the all-purpose flour and quick-cooking oats to the bowl. Mix again until everything is just combined. Be careful not to overmix; you want the mixture to be cohesive but still have some texture.
Set aside one heaping cup of the oat mixture. This will be used for topping later. Press the remaining oat mixture evenly into the bottom of the prepared baking dish, creating a sturdy and even crust. Bake this crust for 10 minutes in the preheated oven.
While the crust is baking, prepare the filling. In a separate bowl, combine the sweetened condensed milk and creamy peanut butter. Mix until the two ingredients are fully blended and creamy. This filling is sweet, rich, and oh-so-delicious.
Once the crust is done baking, remove it from the oven. Pour the peanut butter filling over the warm crust, using a spatula to spread it out evenly. This ensures every bite is packed with flavor.
Take the reserved oat mixture and sprinkle half of it over the peanut butter layer. Then, generously sprinkle the Reese’s Pieces candies over the top. This adds color and a delightful crunch that’s hard to resist.
Top with the remaining oat mixture, spreading it evenly over the candies to create a nice topping. Bake the assembled bars for about 25 minutes, or until golden brown and set.
Once baked, remove the bars from the oven and allow them to cool in the pan. After about 30 minutes, you can lift them out using the foil and cut them into squares. They’ll be warm, gooey, and packed with flavor!
Store the cooled bars in an airtight container at room temperature, or in a zip-top bag for easy snacking throughout the week.
