Heat oven to 350F. Line a baking sheet w/ parchment paper or a nonstick silicone baking mat. In a bowl, combine peanut butter, sugar, and egg until well blended. Using a tablespoon, scoop out dough and roll into balls. Place on prepared baking sheet about 2” apart. Using tines of a fork, make a crosshatch in the top. Bake until browned and set, about 10 minutes. Remove baking sheet to a rack to cool, letting the cookies cool on the baking sheet. (If using the canned chickpea liquid, it is important to let the cookies cool a full 10 minutes before moving them off the baking sheet.) Store in a sealable airtight container for up to 1 week.