Step 1

Heat oven to 350F. Line a 15×10×1-inch pan with foil. Spread peanuts in pan. Bake 6 to 10 minutes, stirring occasionally, until light brown. Pour into small bowl; set aside. Set aside pan with foil to use later.

Step 2

Meanwhile, in a 2-quart heavy saucepan, cook granulated sugar, brown sugar, butter and water over medium-high heat 4 to 6 minutes, stirring constantly with a wooden spoon, until mixture comes to a full boil. Boil 10 to 15 minutes, stirring frequently, until candy thermometer reaches 300F or a small amount of mixture dropped into cup of ice forms a hard brittle strand.

Step 3

Stir in ½ cup of the peanuts; immediately pour toffee into same foil-lined pan. Quickly spread the mixture to ¼-inch thickness with a rubber spatula. Sprinkle with chocolate chips. Let stand for about 1 minute or until chips are completely softened. Spread softened chips evenly over toffee. Sprinkle with remaining peanuts.

Step 4

Refrigerate about 30 minutes or until topping is firm. Break into 2×1 inch pieces. Store in tightly covered container.