Pop the corn, 1/2 cup at a time, in an open wire popper or in a covered pan, using 1 tbsp of oil with each popping.
Pour the popped corn into a very large buttered bowl.
Melt the butter in a large saucepan.
Add the sugar, molasses, and salt.
Bring to the boil.
Cover and cook 3 minutes.
Remove lid and continue cooking over moderate heat to the hard-ball stage (260 degrees).
Immediately pour over the corn, stirring the corn all the time with a large spoon to mix in the syrup.
Butter your hands generously and shape the popcorn into about 36 balls.
Wrap in waxed paper.