Combine sugar, syrup and water in heavy pan. Stir over medium heat, cooking until the sugar dissolves. Cover and cook 3 minutes. Remove cover and cook to soft ball stage (234° F).

Add the peanuts and stir. Cook until brittle reaches hard crack stage (300° F), stirring frequently but not constantly. The sugar mixture should develop a golden brown color from the sugars caramelizing, and it needs the right balance of sitting and stirring to accomplish that. Do not allow the temperature to go over 300 as this can break down the sugar structure and leave it weak and spongy

Remove from heat and add the salt, baking soda, vanilla, and butter. Stir until well blended. Spread onto a well buttered cookie sheet, working fast. If you want very thin candy, loosen the edges and stretch as thin as possible before it cools. Break into pieces and store in an airtight container.