Preheat your oven to 350°F (180°C). Line an 8x8 inch pan with parchment paper and lightly grease.
In a bowl, whisk together the 1 cup vanilla Greek yogurt (or Skyr yogurt with vanilla extract), 1 large egg, ½ cup peanut butter (or almond butter for variety), ⅓ cup cocoa powder, and ½ cup granulated sweetener (like stevia or monk fruit).
Optional: Stir in ½ cup sugar-free chocolate chips.
Pour the batter into the prepared pan and bake for 35-40 minutes, or until a toothpick comes out slightly crumbly.
Let cool, sprinkle extra chocolate chips on top (if desired), and enjoy the soft, mousse-like texture.
