Line a 9x5-inch loaf pan with parchment paper.
In a high-speed blender or food processor, add the walnuts and blend until finely chopped. Use a rubber spatula to scrape under the blade. Add the remaining ingredients and pulse/blend until thoroughly combined. After the first blend, you’ll likely need to use a rubber spatula to scrape underneath the blade again to make sure everything is mixed in and then blend once more.
Transfer the mixture to your loaf pan and press into one even, compact layer.
In a medium bowl mix together the peanut butter, maple syrup, coconut oil, and salt (if using). Depending on the thickness of your peanut butter, you may need to thin it out with more coconut oil until it’s spreadable.
Spread the peanut butter mixture on top of the brownies. Top with chopped peanuts and flaky salt (if using). Lightly press the peanuts into the peanut butter so that they stick.
Let chill in the freezer for at least 2 hours or until the peanut butter “frosting” has firmed up. Store in an airtight container in the fridge for up to 7 days or in the freezer for up to 3 months.
I like these best out of the freezer. You be the judge!