Line a 13-in. x 9-in. pan with foil; coat the foil with cooking spray and set aside. Butter the sides of a large heavy saucepan with 2 teaspoons butter. Cube remaining butter; place in pan. Add the sugar, water and corn syrup. Cook and stir until mixture turns golden brown and a candy thermometer reads 300° (hard crack stage)., Remove from the heat; stir in hazelnuts. Pour into prepared pan without scraping; spread evenly. Let stand at room temperature until cool, about 1 hour., In a microwave, melt chocolate chips; stir until smooth. Spread evenly over toffee. Sprinkle with hazelnuts, pressing down gently. Let stand for 1 hour. , Break into bite-sized pieces. Store in the refrigerator.