Don't remember where I got this one, but it's pretty basic. Only potential problem is it calls for raw salted peanuts.
3 cups granulated sugar
1 cup light corn syrup
1/2 cup water
3 cups salted peanuts (raw, not roasted)
1/2 cup (1 stick) unsalted butter, plus 3 tablespoons for greasing pan
1 teaspoon pure vanilla extract
1 teaspoon baking soda
1 teaspoon sea salt
1. Combine the baking soda and salt in a small bowl. Set aside.
2. Butter the bottom and sides of a large rimmed baking sheet and set aside.
3. In a large saucepan, combine the sugar, corn syrup, and water. Attach a candy thermometer to the pan and cook mixture over medium heat until 240 degrees F (thread stage). Stir in the peanuts and continue cooking, stirring constantly with a silicone spatula until the mixture is golden and reaches 300 degrees F (hard crack stage).
4. Remove from heat and stir in the 1 stick of butter. Add the vanilla, baking soda, and salt. Stir until ingredients are combined and the butter has melted.
5. Quickly pour and spread the mixture into the prepared baking sheet.(Be careful not to touch the mixture to your skin.) Let cool completely (about 1 hour), then break the brittle into several pieces. Store in an airtight container.