Soda Water to top up (chilled)
Take a highball glass and mix 2 parts gin, 1 part lemon juice and half a part simple syrup. Stir with a long cocktail spoon. Now fill the glass with ice and top it up with soda water. Stir again. The classic garnish would be a lemon wheel and a maraschino cherry. The way Robert De Niro likes his favourite drink, for example, in Meet the Parents.