Equipment Needed
- A stand mixer or electric hand mixer
- A 10×15 inch jelly roll pan (This size is key for the right thickness!)
- Parchment paper
- Mixing bowls
- Sifter or fine mesh strainer
- Spatula
Step-by-Step Instructions
We start with the glorious peanut butter base. Preheat your oven to 350°F (175°C) and line your 10×15 inch jelly roll pan with parchment paper, letting it overhang on the sides for easy lifting later. In the bowl of your stand mixer, cream together the softened butter, both sugars, and the 2 cups of peanut butter on medium speed until the mixture is light, fluffy, and completely smooth. This takes a good 3-4 minutes. Scrape down the sides of the bowl, then beat in the vanilla and eggs, one at a time, until just combined.
In a separate bowl, whisk together the flour and baking soda. With your mixer on low speed, gradually add the flour mixture to the wet ingredients, mixing just until no dry streaks remain. Then, using a sturdy spatula, fold in the old-fashioned oats by hand. The dough will be thick, slightly sticky, and incredibly fragrant. Transfer the dough to your prepared pan. Using your fingers or the bottom of a measuring cup dusted with flour, press the dough firmly and evenly into every corner of the pan. An even layer is crucial for consistent baking.
Bake the base for 15-18 minutes. You’re looking for the edges to be set and just starting to turn a light golden brown. The center will still look slightly soft, but it will set as it cools. Do not overbake! Overbaking will make the bars dry and crumbly. I set a timer for 15 minutes and check. Remove the pan from the oven and place it on a wire rack. Let the base cool completely in the pan. This patience is essential—if you frost a warm base, the frosting will melt into a puddle.(See the next page below to continue…)