Special equipment: a nonstick silicone liner; a candy thermometer
Preheat the oven to 350 degrees F. Line a baking sheet with a nonstick silicone liner and coat it with cooking spray. Set aside.
On another baking sheet, roast the hazelnuts until fragrant, 10 minutes. Remove them to a plate.
Combine the butter, sugar and salt in a medium saucepan and bring to a boil, whisking until melted. Cook, whisking occasionally, until the mixture registers 300 degrees F on a candy thermometer. Immediately remove from the heat and stir in the hazelnuts. Pour the mixture onto the prepared baking sheet and smooth with an offset spatula. Let dry for about 1 1/2 minutes, then scatter the chocolate chips on top. As they melt, spread the chocolate to the outer edges of the toffee with an offset spatula. Sprinkle with sea salt and freeze until set, about 30 minutes. Peel the toffee away from the silicone liner and transfer to a cutting board. Cut into pieces with a sharp knife. The toffee will keep, tightly covered, up to 1 week.
Recipe adapted from "One Dish at a Time: Delicious Recipes and Stories from My Italian-American Childhood and Beyond" by Valerie Bertinelli © Rodale 2012. Provided courtesy of Valerie Bertinelli. All rights reserved.