Preheat the oven to 425 degrees F. Put a large bowl in the freezer to whip the cream.
In a small saucepan over medium heat, combine the water, butter, and salt and bring it to a boil. Reduce the heat, add the flour and cinnamon all at once, stirring vigorously with a wooden spoon. Cook until the mixture forms a ball, has a slightly sweaty sheen to it, and has pulled away from the sides of the pan. Transfer the mixture to a bowl and let it cool for 3 to 4 minutes. It does not have to be cold, just cool enough so the eggs don't cook when you add them. Using an electric mixer or lots of good old fashioned elbow grease, beat in the eggs 1 at a time. Do not add the second egg until the first is fully incorporated.
Transfer the mixture to a pastry bag equipped with a large straight tip and pipe 1-inch balls onto a sheet tray lined with parchment paper. Be sure to leave at least 1-inch between each of the balls, they grow! When done, dip your finger in water and smooth the top of each ball where the pastry tip was removed. Bake for 20 to 25 minutes, rotating the tray halfway through the cooking time to insure even browning. The puffs should be light, airy, and dry inside. Cool on a rack.
Put the heavy cream into the cold bowl and whip it to stiff peaks with a head mixer. Put the mascarpone in a large bowl and gently mix in the praline paste. When the praline paste is combined, begin to fold in the whipped cream. When the whipped cream is fully incorporated, spoon the mixture into a clean pastry bag. Cut the tops off each profiterole and fill with the mascarpone mixture. Replace the tops and drizzle with the warm chocolate sauce. Transfer to a large serving platter and garnish with chopped hazelnuts.
Fill a medium saucepan with 2-inches of water and put it over medium heat. In a bowl large enough to sit on the saucepan without the bottom touching the water, add the chocolate, cream, butter, corn syrup, and cinnamon. Stir until the chocolate has melted and everything is combined. This is a pretty quick process. When the chocolate is melted, remove it from the heat, and spoon it over the filled profiteroles. This is best served warm!