1 1/2 c. sugar
1 3/4 c. white syrup (Karo)
2/3 c. cold water
3/4 lb. + uncooked peanuts (shelled but not skinned)
1 tbsp. butter
3/4 tsp. baking soda

Boil sugar, syrup and water until it will crack when dribbled in cold water. (Use a cup of water almost ice cold for testing. The candy will string a hair in the air below the spoon at this point.) Add peanuts and butter and stir hard until it turns a brown color. The candy and peanuts will be close to the same color. Add soda "dissolved" in a tablespoon of water, mix well and immediately pour out on lightly greased aluminum foil (about 3 to 4 feet long). Crack candy into pieces when completely cool. (If you prefer lighter candy, use up to 2 teaspoons soda, but be sure to mix it well and pour the candy out as quickly as possible.)

I use closer to a pound of peanuts or as many as I can get in and still stir the candy.