In a small saucepan, heat about ¼ cup (50 grams) sugar over medium heat, stirring frequently, until sugar is melted. Gradually add remaining sugar, about ¼ cup (50 grams) at a time, stirring between each addition until completely melted. Cook until sugar is a deep amber color, 3 to 5 minutes. Remove from heat; stir in hazelnuts and salt. Immediately pour onto prepared pan, quickly spreading into an even layer. Let stand at room temperature until completely hard and set, at least 2 hours. Break into pieces as desired, and store at room temperature in an airtight container for up to 1 week.