Juice your lemon, measure the juice and add it to a cocktail shaker.
1 ounce lemon juice
Add the simple syrup to the cocktail shaker.
½ ounce simple syrup
Add the gin to the cocktail shaker.
2 ounce gin
Fill the shaker with ice, and also add ice to your serving glass.
Give the cocktail shaker about 15-20 good shakes, and then strain the drink into your prepared cocktail glass.
Top the drink off with seltzer.
2 ounce seltzer
Using a cocktail pick, thread it through one side of your lemon slice, then through the Maraschino cherry, and then back through the lemon slice to create your garnish.