I think this is the one you want. 1 C margarine, 2C Brown Sugar-packed, 1/2 C light corn syrup, 1t salt, 1/2 t baking soda, 1t vanilla, 6-8 quarts popped corn. ( I use a large enamel roasting pan and just enough popped corn to almost fill it up.)
Melt margarine, add sugar, syrup & salt. Bring to a boil, stirring constantly. Boil 5 minutes without stirring. Remove from heat, add soda & vanilla. Pour over corn & mix well. Bake at 250 degrees for 45 minutes, stirring every 15 minutes. Remove from pan and let cool. I spill mine on the counter and spread it out until it sets. Make lots, it goes fast.