2) Combine the water, butter, 1 1/2 tsp of sugar and the salt in a heavy medium saucepan. Bring to the boil, stirring until the butter melts. Add the flour and stir over medium heat for 1 minute. Cool for 5 minutes.
3) Crack 2 eggs into a measuring cup. Use a wooden spoon to beat the eggs into the dough, 1 at a time. Spoon 10 or 12 (4cm) mounds of dough onto the prepared baking sheet, spacing them 2.5cm apart. Beat the remaining egg in a small bowl to blend.
4) Gently brush the egg over the dough mounds (do not drip the egg onto the baking sheet). Bake the pastries until they are amber brown, about 50 minutes. Allow them to cool completely before filling.
5) Mix the mascarpone, ricotta, vanilla and remaining 3 tablespoons of sugar in a medium bowl. Refrigerate until cold. Using a serrated knife, cut the tops off the profiteroles and set aside. Spoon the mascarpone mixture into the profiteroles and replace the tops.
6) Combine the chocolate-hazelnut spread and cream in a small bowl. Heat in the microwave for about 30 seconds until warm. Stir the mixture. Spoon the chocolate-hazelnut sauce on top of the profiteroles. Sprinkle with the hazelnuts and serve.