Combine buttermilk, butter and sugar in a 2-quart saucepan. Cook and stir over low heat until sugar is dissolved. Add peanuts and cook over medium heat to soft-ball stage or 238F, stirring constantly. Remove from heat. Add soda, vanilla, and peanut butter. Stir rapidly until mixture is creamy and thickened. Drop rapidly from a tablespoon onto lightly greased waxed paper, forming patties. Let stand until cool and set.
Cajun Country -- New Iberia, Louisiana