Line a 17x11-inch jelly roll pan or large rimmed baking sheet with parchment paper. Lightly grease the paper with non-stick cooking spray and set aside.

Place the granulated sugar and cornstarch in a large, heavy-bottomed saucepan. Whisk thoroughly until combined and free of lumps.

Add the light corn syrup, water, and butter. Cook over medium-high heat, stirring gently until the butter melts and the mixture is combined.

Bring the mixture to a full rolling boil, stirring occasionally. Stop stirring once it boils. Attach a candy thermometer and cook until the syrup reaches 250°F (121°C).

Remove the saucepan from the heat immediately. Carefully stir in the vanilla extract and powdered drink mix until fully dissolved and evenly colored. For two flavors, divide the mixture into separate bowls.

Pour the hot syrup onto the prepared pan and spread it into an even layer. Let it cool for about 20 minutes, until cool enough to handle but still pliable.

For a lighter, airier texture, grease your hands and pull the taffy into a long rope. Fold it back onto itself and continue pulling and folding for 5–10 minutes, until lighter in color and more opaque.

Roll the pulled taffy into a long rope and cut it into bite-sized pieces with greased kitchen shears. For denser taffy, skip pulling and cut the cooled flat taffy into squares with a greased pizza cutter or knife.

Wrap each piece individually in a small square of parchment paper. Store in an airtight container at room temperature.