Combine brown sugar, white sugar and ΒΌ c. water in large, heavy saucepan. Cook and stir over medium heat until syrup reaches 270 degrees (soft crack stage) on candy thermometer. Remove from heat; stir in peanuts and butter. Combine vanilla, baking soda and water; stir into syrup until mixture foams. Pour at once into a buttered jelly roll pan (15 x 10 x 1 inch). Cool completely; break into pieces.