In a saucepan over medium heat, combine equal parts water and granulated sugar, stirring until the sugar dissolves. Add sliced jalapeños and fresh cilantro, then simmer for about 5 minutes until the flavors meld beautifully. Remove from heat and let the syrup cool completely before straining out the solids.

While the syrup cools, prepare fresh lime juice for the margarita.

Gather a cocktail shaker and fill it with ice cubes. Pour in the cooled jalapeño cilantro simple syrup and the freshly squeezed lime juice. Then, gently add tonic water to the shaker.

Prepare your glasses by rimming them with a salt or sugar mixture using a lime wedge.

After shaking, strain the margarita mixture into the prepared glasses filled with ice. Garnish each drink with a slice of lime or a jalapeño float.