1. Lightly butter a cookie sheet; set aside. Stir together cocoa and baking soda in small bowl; add butter. Set aside.
2. Stir together sugar, corn syrup and whipping cream in heavy 2-quart saucepan. Cook over medium heat, stirring constantly until sugar is dissolved. Stir in peanuts. Continue cooking, stirring frequently, until mixture reaches 300°F. on candy thermometer or until syrup, when dropped into very cold water, separates into threads which are hard and brittle. (Bulb of candy thermometer should not rest on bottom of saucepan.)
3. Remove from heat; stir in cocoa mixture. Immediately pour onto prepared cookie sheet. With tongs or wooden spoons, quickly spread and pull into 1/4-inch thickness. Place cookie sheet on wire rack; cool completely. Snap into pieces; store in tightly covered container. About 1 pound candy.