Heat oven to 325°F and line an 8 x 8-inch pan with parchment paper, leaving an overhang for easy removal.
Add all ingredients except the peanut butter chips to a large bowl. Beat with a hand mixer until smooth, then gently fold in the chips with a spatula.
Spread batter evenly in the pan and bake for 18 to 25 minutes until the edges are lightly golden and the center is set with very little jiggle.
Remove bars from the oven and let cool completely in the pan so they fully set.
Optional: For extra peanut butter flavor, place 1/4 cup peanut butter in a small resealable bag, snip a small corner, and drizzle over the bars.
Lift out using the parchment and cut into 16 bars with a sharp knife.
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Notes
Note 1: While these bars use naturally gluten-free ingredients, always check labels to be sure they were not processed in facilities that handle gluten. For guaranteed gluten-free bars, use certified gluten free products.Note 2: To make oat flour, blend whole oats in a blender or food processor until they look like flour. Measure after blending, not before.Storage: Let the bars cool fully, then wrap each one on its own in plastic wrap. Keep them at room temperature for 2 to 3 days or store in the fridge for up to 1 week.