Preheat your oven to 180°C (350°F). Line your 9x9-inch pan with parchment paper, leaving some overhang for easy removal.
In a large mixing bowl, combine the peanut butter, melted butter, and brown sugar. Use a spatula to stir until the mixture is smooth and fragrant, with a creamy, slightly sticky texture.
Add the eggs and vanilla extract to the bowl, then whisk or stir vigorously until everything is well incorporated, and the mixture becomes glossy.
Stir in the old-fashioned oats, baking soda, and a pinch of salt, folding gently to combine. The mixture will start to thicken and become a bit sticky.
Gently fold in the chocolate chips, distributing them evenly throughout the batter, but don’t overmix to keep the texture rustic.
Using a spatula, spread the batter into your prepared pan, pressing it down evenly with gentle pressure to ensure a compact, cohesive layer.
Bake in the oven for about 15 minutes, or until the edges are golden brown and the center is just set, filling your kitchen with a warm, nutty, chocolatey aroma.
Remove the pan from the oven and let the bars cool in the pan for at least 20 minutes; this helps them firm up and makes slicing easier.
Once cooled, lift the bars out of the pan using the parchment overhang and transfer to a cutting board. Slice into squares and enjoy!
Store leftovers in an airtight container at room temperature for up to 3 days for the best chewy texture and flavor.