First, make the strawberry simple syrup. I like to make this the day before, but at the very least make the syrup 1 hour before making the cocktails.
Chop up the strawberries and add them to a saucepan with the sugar and water. Mix together and bring everything to a simmer, stirring frequently. Cook at a simmer for about 5 minutes until the strawberries begin to break down and the syrup turns pink.
Remove the simple syrup from the stove, let cool, and add to a closed container. Place the container in the fridge for at least 1 hour to chill and to continue infusing with the strawberries. Do not strain the strawberries out.
Once the syrup has finished chilling, make the cocktails.
To make one cocktail add 3 Tbsp of the strawberry simple syrup and 4 mint chopped mint leaves to a glass. Muddle together with a muddler. Then, fill the glass with ½ cup crushed ice, 1 Tbsp lemon juice, 3 oz sparkling water, and 1.5 oz rum.
Garnish each cocktail with an additional sliced strawberry or mint. Then, serve and enjoy!