Line two baking sheets with parchment or wax paper and set aside. Fit a stand mixer with the whisk attachment.

In a medium saucepan, combine sugar, corn syrup, water, and salt. Stir over medium heat until the sugar dissolves and the mixture looks clear.

Attach a candy thermometer and cook without stirring until the syrup reaches 260°F (hard-ball stage). If you do not have a thermometer, use the cold water test: a small drop in cold water forms a firm, pliable ball.

While the syrup cooks, beat the egg whites in the mixer bowl on high speed until stiff peaks form.

With the mixer running on medium-high, slowly stream the hot syrup down the side of the bowl into the egg whites. Avoid pouring directly onto the whisk.

Sprinkle in the dry Jello powder and add vanilla (if using). Beat 5–7 minutes until thick, less glossy, and the mixture holds its shape.

If desired, fold in finely chopped nuts using a spatula.

Working quickly, drop spoonfuls of the candy onto the prepared sheets.

Let stand at room temperature until firm and dry to the touch, about 1–2 hours (longer if humid). Store in an airtight container at room temperature for up to 5 days.