Place nuts in a plastic storage bag and crush into small pieces with a meat tenderizer.
In a bowl, whisk together the egg and brown sugar. Mix in peanut butter and Nutella.
Fold in nuts.
Scoop small pieces of dough onto a lined baking sheet. Using a fork, press on the tops lightly to flatten out.
Bake cookies at 350°F for 8-10 minutes. They will still appear soft when you remove them from the oven, but that's perfectly normal. Allow them to set at room temperature for a couple minutes to harden. Serve and enjoy!