Preheat your oven: Begin by preheating your oven to 350°F (175°C). Grease a 9x13 inch baking dish and set it aside to prepare for the cookie bars.
Cream the butter and sugars: In a large bowl, cream together 1 cup of softened unsalted butter, 1 cup of granulated sugar, and 1 cup of packed brown sugar until the mixture is light and fluffy. This should take about 2-3 minutes with an electric mixer.
Add peanut butter and eggs: Next, add 1 cup of creamy peanut butter, 2 large eggs, and 2 teaspoons of vanilla extract to the creamed butter and sugar mixture. Beat everything together until it is well combined and smooth.
Mix dry ingredients: In another bowl, whisk together 2 cups of all-purpose flour, 1 teaspoon of baking soda, and 1/2 teaspoon of salt. Ensure there are no lumps in the flour for even mixing.
Combine wet and dry ingredients: Gradually add the dry ingredients to the wet mixture, mixing gently until just combined. Avoid over-mixing to maintain the tender texture of the bars.
Stir in oats: Fold in 2 cups of quick oats until they are evenly distributed throughout the cookie dough.
Spread the mixture: Transfer the cookie dough into the prepared baking dish, spreading it evenly with a spatula to ensure uniform baking.
Bake: Place the dish in the oven and bake for 20-25 minutes. The edges should turn golden brown, and a toothpick inserted into the center should come out clean. Keep an eye on them towards the end to avoid over-baking.
Cool completely: Once baked, allow the cookie bars to cool completely in the baking dish before cutting them into squares. This helps set the texture and makes them easier to slice.