In a food processor, crush the graham crackers or Biscoff cookies if using (you should need about 3 of the full rectangular crackers) until they are a fine dust.
If using Peanut Butter Powder (which is my preferred method these days) you may only need 2 Tbsp depending on the type of peanut butter you are using. So start with that much and add more as you need.
Combine peanut butter, powdered sugar and graham crackers or Biscoff cookies or Peanut Butter Powder using a hand mixer. The mixture should be soft but not sticky. A lot like Play-Doh! As long as you can easily roll it into a ball and it doesn't fall apart. If it's to crumbly, add more peanut butter. If it's too soft and sticky, add more powdered sugar / cracker crumbs / peanut butter powder.
Use a tablespoon to scoop out some of the peanut butter mixture (about 15 - 18g worth). Roll it into a ball, and then flatten it into a patty that's slightly smaller than the bottom of your muffin liner. You can do this by hand, or you can add the ball to a parchment lined baking sheet. Then top it with a small piece of wax or parchment paper and press down with something flat and hard (I used a small glass bowl).
Once all patties have been formed, add them to the freezer to firm up for about 20 minutes.