Baked Caramel Corn

Melt margarine. Stir in sugar, corn syrup, and salt. Bring to a boil, stirring constantly. Boil for 5 minutes without stirring. Remove from heat and add baking soda and vanilla. Gradually pour over corn and mix to coat well. Turn out into 2 baking pans. Bake at 250 for one hour, stirring every 15 minutes. Remove from oven. Cool completely. Break up pieces. Store in airtight containers.