Unsalted butter, room temperature, for baking sheet
1-1/2 c sugar
34 c cold water
½ c light corn syrup
pinch of salt
2-1/2 c unsalted dry-roasted peanuts
1 t vanilla
1 t baking soda
vegetable oil, for spatula.

Butter a 9×13 inch rimmed baking sheet, set aside.
In a medium saucepan, bring sugar, water, corn syrup and salt to a boil over medium-high heat, stirring until sugar has dissolved.
Continue cooking, without stirring, until mixture reaches soft-ball stage (238-240 degrees), swirling pan occasionally; wash down sides of pan with a pastry brush dipped in water. Stir in nuts and continue cooking, stirring frequently to prevent nuts from burning, until mixture is light amber.
Remove pan from heat; carefully stir in vanilla and baking soda. (Mixture will foam up in pan.) Pour onto prepared baking sheet, quickly spread into a ½ inch thick layer with an oiled metal spatula. Let stand until completely cool.
Break brittle into large pieces and store in an airtight container up to one month.