Mix water, karo syrup, and white sugar in a saucepan. Bring to a boil until it cracks when tested in cold water. (approx. 20-30 minutes or using candy thermometer, until it reaches 234 degrees) Syrup appears light tan in color.
Add: peanuts. Continue boiling another 20+ minutes, or until temperatures on the candy thermometer reaches 310 degrees. Color will be medium/dark tan. Do not overcook past 310 degrees, it will taste burnt. If it is cooked under 310 degrees, it will be sticky.
Prepare 2 large cookie sheets by buttering the surfaces. slightly overlap the cookie sheets at the ends.
Prepare the following 4 ingredients ahead o time: When the temperature of above mixture reaches 310 degrees, each of the following four ingredients will need to be added, in order, as quickly as possible. Mix in each ingredient, stir continuously, with baking soda being the last ingredient added.
2 tsp. vanilla
2 tsp. butter
2 tsp. baking soda
Soda must be the last ingredient added. Stir soda in the mixture, beating well (about 1 minute). Mixture will puff up in volume. This is natural.
Pour over surface of cookie sheets immediately. Let cool 30 minutes or more. Break into desired size pieces.