2 ounces gin
½ - ¾ ounce lime juice
3 to 4 ounces of Topo Chico Mineral Water
half of a squeezed (hollowed out) lime shell as garnish (traditional; you can also substitute a lime slice or wheel)
Add lime juice to the serving glass (traditionally, you squeeze the juice of half a lime directly into the glass). Toss in the hollowed out lime shell, if using. Add gin and several ice cubes.
Top up the glass with Topo Chico Mineral Water. Stir once or twice to mix. If you aren’t using the lime shell, add a couple of lime slices to the glass (and perhaps garnish the rim with a lime slice or wedge). Serve.