This a great and classic Gin recipe
It was actually created by John Collins who was a bartender at Limmer's Hotel in London. It caught on heavy in the U.S. in 1950s suburbia.
2 oz Gin
1 oz Lemon Juice
1/2 oz Simple Syrup
3 oz Club Soda
Garnish with a Lemon Slice and Maraschino Cherries