In a large bowl, stir together the peanut butter and maple syrup (or honey) until smooth and well combined. If the mixture feels too thick, a quick microwave warm-up (about 15 seconds) will help loosen it up.
In another bowl, combine oats and all the mix-ins of your choice.
Combine the maple syrup peanut butter mixture with the mix-ins. Stir well until everything is evenly coated and sticks together.
Line an 8x8 or 9x9 baking dish with parchment paper. Pour in the mixture and press it firmly into the pan using the palm of your hands or the bottom of a jar. The firmer you press, the better your bars will hold together.
Refrigerate for 1 hour, or until firm enough to slice. If you’re short on time, pop them in the freezer for 20 minutes.
Once set, lift the parchment paper out, place on a cutting board, and slice into bars or squares. Store them in an airtight container in the fridge for up to a week.
Notes
The Mix-Ins here are what I used in the photos shown in this post. You can choose any of your favorites to customize these granola bars to be your own. The total amount should add up to be about 2 cups.