
Combine brown sugar, butter, syrup, vanilla and salt in saucepan.
Boil 5 minutes, stirring occasionally.
Remove from heat and stir in soda and cream of tartar (stir quickly) and pour over popped popcorn in a large mixing bowl. Mix well.
Spread onto baking sheets or roasting pan.
Bake at 250 degrees for 1 hour, stirring occasionally.
Remove from oven and turn onto waxed paper to cool.
Store in airtight container.