1. Line an 11-by-17-inch baking sheet with parchment paper and set aside.
2. In the top of a double boiler, melt chocolate, stirring constantly.
3. Stir hazelnut extract and Nutella into the melted chocolate. Remove from heat, and pour the mixture onto the prepared baking sheet; spread evenly. Sprinkle with chopped hazelnuts.
4. Chill until firm, 25 to 30 minutes. Break into pieces, and serve. Store in an airtight container in the refrigerator for up to one week.
Note-you can also melt the chocolate in the microwave.