1. Prepare the Crust:

1. Preheat oven to 350°F (175°C). In a small saucepan, melt the sugar over medium heat until it turns into a golden caramel. Pour the caramel into a 9-inch round baking dish, tilting to coat the bottom evenly.
2. In a blender, combine eggs, condensed milk, evaporated milk, vanilla extract, and cocoa powder. Blend until smooth.
3. Pour the mixture over the caramel in the baking dish. Sprinkle the chopped Ferrero Rocher chocolates and hazelnuts (if using) evenly on top.
4. Place the baking dish in a larger roasting pan and fill the roasting pan with hot water until it reaches halfway up the sides of the baking dish.
5. Bake for 45-50 minutes or until the flan is set. Remove from the oven and let it cool to room temperature, then refrigerate for at least 4 hours or overnight.
6. To serve, run a knife around the edges of the flan and invert onto a serving plate. Slice and enjoy!