Wash all fruit thoroughly and spread on paper towels. Allow to air dry for at least 30 minutes, then pat completely dry with fresh paper towels. Any surface moisture will prevent the sugar coating from adhering properly.

Thread 2 strawberries or 3–4 grapes onto each bamboo skewer, leaving about 3 inches at the bottom as a handle. Place skewers on a parchment-lined baking sheet and set aside.

Combine sugar, water, and cream of tartar (if using) in a medium, heavy-bottomed saucepan. Stir gently just once to combine, then stop stirring entirely.

Clip a candy thermometer to the side of the pot. Bring the mixture to a boil over medium-high heat. As the syrup cooks, brush down the sides of the pot once or twice with a wet pastry brush to dissolve any rogue sugar crystals, but do not stir the syrup.

Cook the syrup until it reaches 300–310°F (hard crack stage), approximately 10–15 minutes. The syrup should be a very pale golden amber color. Watch carefully in the final minutes — temperature rises quickly.

Remove the pot from heat immediately when the syrup reaches 300–310°F. Tilt the pot to create a deeper pool of syrup for easier dipping.

Working quickly, dip each fruit skewer into the hot syrup, rotating to coat all fruit evenly. Hold the skewer over the pot for 2–3 seconds to allow excess syrup to drip off.

Immediately lay the dipped skewer flat on the prepared parchment-lined baking sheet. The sugar will set and harden within 30–60 seconds.

Repeat with remaining skewers. If the syrup becomes too thick or begins to set in the pot, briefly return it to low heat for 1–2 minutes to loosen.

Serve Tanghulu within 2–4 hours for maximum crispness. Do not refrigerate.