2 cups sugar
1 cup white corn syrup
1/2 cup water
2 tablespoons butter
2 cups salted peanuts
1 teaspoon vanilla extract
1 tablespoon baking soda

Grease a 15 X 10-inch jelly-roll pan and set aside.
Combine sugar, corn syrup, and water in large heavy saucepan. Bring to a boil, stirring, until sugar is dissolved. Boil to 260° on candy thermometer (very hard-ball stage), stirring occasionally with wooden spoon. Add butter and peanuts. Continue boiling to 310°, stirring constantly with wooden spoon. Syrup will turn a very deep golden color.

Remove from heat and add vanilla and soda. Stir quickly, as candy becomes very foamy. Immediately pour in prepared pan and spread as thin as possible with spoon. Cool thoroughly, then use a rolling pin or meat mallet to crack. Turn out of pan and break into smaller pieces. Store in tightly covered container. Makes about 2 pounds of peanut brittle.

Source: http://southernfood.about.com/od/candyrecipes