Butter a large jelly roll pan or a cookie sheet with sides really well.
In a medium saucepan, stir together the sugar and cornstarch.
Add corn syrup, water, butter, and salt and stir well until butter is melted.
Bring to a boil over medium heat and stop stirring. Cook the mixture until the candy thermometer read 250 degrees F (120 degrees C). This takes some time to get it to 250 degrees. Once the temperature approaches 250 degrees, watch very closely because it cooks quickly at the end.
Immediately remove from heat.
Carefully stir in vanilla and drink mix.
Stir well. We should have stirred ours more-- notice some bits of drink mix (dark spots) on our taffy.
Pour mixture onto a buttered baking pan.
Allow it to cool enough to handle, about 15 minutes.
Once the taffy has cooled enough to handle, butter hands, and begin pulling. (It starts kind of translucent)
Then pull...and pull...butter hands again...pull... and stretch...pull...more hand buttering...pull...
It will become opaquer and lighten in color.
This takes about 10-15 minutes of pulling.
Pull into long ropes and cut with buttered scissors.
Wrap pieces of taffy in pieces of waxed paper and give it a good twist on each end.