In a small heatproof bowl or cup, combine the granulated sugar (2 tbs) and hot water (2 tbs). Stir until the sugar is fully dissolved to form a quick simple syrup. Let it cool briefly (about 1–2 minutes) before using.

Place 2 cups of chilled carbonated lemon-lime soda into a large measuring cup or pitcher. If you want extra fizz, reserve the club soda to add later.

Citrus & Flavor

Add the fresh citrus juices to the soda: 2 tsp lemon juice, 1 tsp lime juice, and 1 tsp orange juice. Pour them in gently and stir once to combine.

If using citric acid for extra tang, dissolve the 1 tsp in the warm simple syrup before adding. Stir the syrup-citric mixture into the soda.

Add the optional 2 drops of green food coloring or 1–2 drops of lemon-lime concentrate, if desired, and stir gently to create the characteristic pale green color. Add coloring incrementally to avoid over-darkening.

Caffeine & Aroma (optional)

If you want to approximate the beverage's caffeine-bitterness profile, stir in 1 tsp of very strong cooled espresso or 1 tsp instant coffee dissolved in 1 tsp water. This is optional — omit for a caffeine-free drink.

Add 1 tsp vanilla extract and stir gently. The vanilla provides a faint roundness and aroma reminiscent of the commercial beverage.

Garnish & Finish

Fill a tall glass with about 1 cup of ice cubes. Pour the prepared soda mixture over the ice.

If you reserved club soda, top with 1/2 cup club soda for extra effervescence and stir once very gently to combine.

Garnish with a lime wheel or wedge on the rim. Serve immediately while fizzy.