Combine sugar, water, butter, corn syrup and salt in a saucepan.

Cook over medium heat, stirring constantly, until sugar is dissolved.

Turn heat down to medium-low and continue to cook without stirring until syrup reaches 270°F (132°C) and a teaspoonful dropped into cold water forms a hard, brittle ball.

Remove from heat and carefully add vanilla extract.

Pour syrup over popped popcorn in a large bowl.

Mix quickly and thoroughly until all popcorn kernels are evenly coated with the syrup.

Grease your hands with butter to prevent sticking.

Dip your palms in the popcorn mixture.

Quickly form the popcorn into balls.

Place popcorn balls on waxed paper to cool and harden.