Combine granulated sugar, dark brown sugar, and light corn syrup in a small saucepan. Add 1/4 cup (60 ml) of water — just enough to dissolve the sugars. Warm the mixture over low heat, stirring constantly, until all sugars dissolve and mixture is clear and slightly thickened (2–4 minutes). Do not boil vigorously. Remove from heat.

Flavor the syrup

Stir the vanilla extract, amaretto or almond extract, cherry juice or grenadine, citrus oil or the finely grated zest of 1/4 lemon/orange (about 1/4 tsp), a pinch of salt, and the cola bitters (if using) into the warm syrup. Taste and adjust: if you want a stronger cherry note, add up to another 1/4 tsp grenadine; for more almond, add a tiny extra drop of extract. Allow the syrup to cool to room temperature (10–15 minutes).

Combine with carbonated water

Measure out 2 cups (about 480 ml) of chilled carbonated water. To one serving, stir in 2 tablespoons (about 30 ml) of the prepared syrup into the carbonated water. Adjust sweetness/strength by adding more syrup 1/4 teaspoon at a time until desired balance is reached. (The recipe quantities above produce a small batch of syrup sufficient for about 6–8 servings when diluted at roughly 2 Tbsp per 8 fl oz.)

If you prefer a single large glass instead of two cups, scale: use 8 fl oz (1 cup) carbonated water with 1 Tbsp syrup as a starting point.

Garnish & Serve

Fill a tall glass with ice cubes.

Pour the soda prepared above over the ice. Give the glass a gentle stir to combine without flattening the carbonation.

Garnish with a maraschino cherry and a lemon or lime wedge on the rim. Serve immediately cold.