Preheat the oven to 350 degrees F (175 degrees C). Grease an 8x8-inch baking dish with cooking spray; line with parchment paper.
Place Nutella(R) in a microwave-safe bowl. Microwave on high until soft and creamy, about 1 minute, stirring every 15 seconds.
Whisk eggs in a bowl with an electric mixer until pale and creamy, about 7 minutes. Mix in Nutella(R) and whisk on low speed until well combined, about 2 minutes. Pour mixture into the prepared baking dish.
Bake in the preheated oven until top is dry and edges have started to pull away from the sides of the pan, about 25 minutes. Let cool completely before slicing.