1. Coat a large, rimmed baking sheet with butter and set it aside. You can use a silicone baking sheet.
2. In a medium, heavy bottomed saucepan over medium-high heat, bring the sugar, corn syrup, wter, and salt to a boil, stirring continuously until the sugar has dissolved, about 5 minutes.
3. Continue cooking, swirling the pan occasionally, until the mixture reaches the hard-ball stage on a candy thermometer (250f to 265f), about 5 minutes. With a pastry brush dipped in water or a heat-resistant silicon spatula, wash down the sides of the pan to keep sugar crystals from forming (adult jobs).
4. Carefully stir in the nuts (the syrup will be very hot!). Continue cooking, striing frequently to prevent the nuts from burning, until the mixture is light amber in color and the nuts are golden brown, about 5 minutes.
5. Remove the pan from the heat. Add the butter and vanilla extract and stir until the butter melted. Carefully stir in the baking soda until combines (the mixture will foam up in the pan), then quickly pour the mixture onto the prepared baking sheet (an adult's job).
6. Using an heat-resistant spatula under the hot candy to loosed the edges and bottom.
7. Let the brittle cool complete, about 60 minutes. Break it into large pieces and store it at room temperature in an airtight container layered between pieces of waxed paper. it will keep for up to a month.