Muddle the diced strawberries and sugar together in a small dish. Let this rest for 10 minutes to allow the sugar to release some of the berries' natural juice. Muddle in the leaves from 1 sprig of mint.
Divide the strawberry mixture between 2 12 oz rocks glasses. Add 2 oz of bourbon to each glass and stir together.
Add 1 large ice cube and 1 mint sprig to each glass. Top of with sparkling water.