Pop popcorn (can use unsalted/buttered microwave). Put brown sugar, butter, corn syrup and salt into saucepan. Cook and stir on medium heat until butter melts and everything is mixed. When mixture boils, stop stirring. Cook 5 minutes without stirring. Remove from heat. Stir in thoroughly baking soda and vanilla. Pour over popcorn. Add peanuts. Stir well until all-popcorn is covered.
Put pan into oven on 300. Bake 15 minutes. Stir. Bake 5-10 minutes longer. Remove from pan and let cool. Easily doubles.