Ingredients

• 12 (4 3/4- by 2 1/2-inch) graham crackers
• 1 1/2 sticks (3/4 cup) unsalted butter, cut into pieces
• 1/2 cup packed light brown sugar
• 1/8 teaspoon salt
• 1 1/2 cups semisweet chocolate chips (9 1/2 oz)
• 1 cup walnuts, pecans, or almonds (3 to 4 oz), chopped
• Special equipment: a small metal offset spatula

Instructions

1. Preheat oven to 375°F. Line a 15- by 10- by 1-inch baking pan with foil, leaving a 2-inch overhang at each end.
2. Line bottom of pan with graham crackers (it will be a tight fit).
3. Melt butter in a 1 1/2- to 2-quart heavy saucepan over moderately low heat, then add brown sugar and salt and cook, whisking, until mixture is smooth and combined well, about 1 minute. Pour over crackers, spreading evenly, and bake in middle of oven until golden brown and bubbling, about 10 minutes.
4. Scatter chocolate chips evenly over crackers and bake in oven until chocolate is soft, about 1 minute. Remove pan from oven and gently spread chocolate evenly over crackers with offset spatula. Sprinkle nuts evenly over chocolate and cool crackers in pan on a rack 30 minutes. Freeze until chocolate is firm, 10 to 15 minutes.
5. Carefully lift crackers from pan by grasping both ends of foil, then peel foil from crackers. Break crackers into serving pieces.