Preheat oven to 350 degrees F (175 degrees C). Line an 8x8 baking dish with parchment and lightly coat with cooking spray.

Place peanut butter cups in a medium microwave-safe bowl and microwave in 30 second intervals, stirring in between, about 2 minutes total, until smooth. Let cool slightly.

Using an electric mixer or whisk, beat eggs until frothy. Slowly drizzle in chocolate while mixing until well incorporated. Pour batter into prepared pan.