1 large red or pink grapefruit
1 lime
2 stalks lemongrass
3/4 C. sugar
1/4 C. honey
Carbonated water

Peel wide strips of zest (avoiding the bitter white pith underneath) from half the grapefruit and the whole lime. Juice grapefruit and lime into a liquid measuring C. (add water to reach 1 C. if needed). Pour into a small saucepan and add zest strips. Cut off green tops from lemongrass (about half the stalk) and peel first two outer layers from stalks. Mash stalks with a meat mallet and cut into 2-in. pieces. Add to pan of juices along with sugar and honey. Heat citrus lemongrass mixture over medium heat until boiling; boil 1 minute, then remove from heat and let cool. Chill overnight, then strain syrup into a glass jar or measuring C., discarding solids. To serve, fill an 8-oz. glass halfway with ice cubes, add 2 tsp. syrup (or more if you like), top with carbonated water, and stir.