Preheat oven to 350 degrees Fahrenheit. Line a 9-inch round baking pan with parchment paper and grease.
With an electric mixer, beat the eggs until tripled in volume and fluffy, about 5 minutes.
Remove the lid and seal from Nutella jar and microwave for 30 seconds to soften. Pour Nutella into a large mixing bowl. Fold the egg mixture gently with a spatula into Nutella, one-third at the time.
Transfer into prepared baking pan. Bake for 20-25 minutes, or until top is set. Cool on a wire rack for 10 minutes then remove from the pan and place on a cake plate.
Mint Chocolate Layer
Meanwhile, in a small bowl, combine water and gelatin and set aside to bloom for 8-10 minutes.
Place the chopped white chocolate in another glass or metal bowl. Set aside.
In a small saucepan, bring heavy cream to a simmer.
Add bloomed gelatin and whisk until fully dissolved, or you can first microwave it for 10 seconds to liquefy. Remove from heat and cool slightly, then pour over the white chocolate, whisking until melted and smooth. Add the mint extract and food coloring, if using. Cool to room temperature.
Spoon the mixture over the cooled cake layer and smooth it out with an offset spatula. Refrigerate while making chocolate ganache.
Chocolate Ganache Frosting
Place the chopped chocolate in a glass or metal bowl. Set aside.
In a small sauce pot, bring cream to a bare simmer. Pour over the chopped chocolate. Let it stand for 1 minute, then stir until the chocolate is melted and the mixture is smooth.
Allow the ganache to cool and thicken slightly for 10 minutes, while remaining pourable. Pour over the mint chocolate layer and smooth the top.
Refrigerate for at least 2 hours. Garnish as desired.
You can use a box mix easily for the cake layer! Mix the box, pour half of it in your 9-inch cake pan, and then make some cupcakes with the rest of the batter or look for a brownie box mix for a 9x9-inch sized pan.
Use good quality chocolate bars - the chocolate baking chips are not suitable for this recipe. If you like a strong mint flavor, add more mint extract.
To color the mint layer green, add first a couple of drops of food coloring (I used AmeriColor gel in forest green) and mix, then add more (drop by drop) until you reach the desired shade.
You might want to put the mint layer into a refrigerator to cool faster, just be careful not to leave it in too long because it will be too hard to evenly spread over the cake.