Preheat your oven to 175°C (350°F) and line your 9-inch square baking pan with parchment paper, letting some overhang for easy removal.
In a large mixing bowl, combine the peanut butter, brown sugar, and melted butter. Use a spatula to stir until the mixture is smooth and fragrant, with a creamy texture.
Add the large egg and vanilla extract to the bowl, then whisk or stir until everything is well incorporated and the mixture feels slightly fluffy.
In a separate bowl, whisk together the rolled oats, baking soda, and a pinch of salt for even distribution.
Gradually add the dry oats mixture to the wet ingredients, stirring gently until just combined. The dough should be thick and sticky, with a slightly textured appearance.
Gently fold in the chocolate chips, distributing them evenly throughout the dough for pockets of melty richness.
Transfer the dough to the prepared pan, pressing it down firmly with a spatula or your fingers to create an even layer. Smoothing the top helps ensure uniform baking.
Bake in the preheated oven for 15–18 minutes, or until the edges turn golden brown and the center feels set but slightly soft when pressed.
Remove the pan from the oven and let the bars cool in the pan for about 10 minutes, allowing them to firm up slightly. Then, lift the bars out using the parchment overhang and transfer to a wire rack.
Allow the bars to cool completely before slicing into squares or rectangles. For cleaner cuts, chill the entire pan in the fridge for 30 minutes beforehand.
Slice into your desired sizes, then enjoy the chewy, gooey texture packed with chocolate and peanut butter flavor.