Prepare a small baking sheet by lining it with aluminum foil. Coat the foil with a thin layer of butter or nonstick cooking spray. Set it aside.
In a heavy-bottomed, medium sauce pan, melt the butter over medium heat. Once it is melted, remove it from the heat and stir in the sugar. Once the sugar is mixed in, add the water and corn syrup and stir until well-incorporated.
Place the pan back on the heat and insert a candy thermometer. Cook over medium-low heat, stirring often, until the candy reaches 290 F.
Working quickly, remove pan from the heat and stir in the cinnamon and 3/4-cup of the chopped nuts, and immediately pour the candy onto the prepared baking sheet. Spread chocolate chips in an even layer over the hot toffee. As the chocolate melts, spread evenly across the surface. Sprinkle remaining hazelnuts evenly over melted chocolate. Allow the toffee to sit at room temperature until it is completely cool.