In a small saucepan, stir together sugar, water and sliced ginger for the simple syrup. Bring to a boil over high heat. Once boiling, remove from heat, cover and steep for 15 to 30 minutes (the longer it steeps, the more intense the ginger flavor becomes!).

Strain out ginger slices and cool syrup completely in an airtight container. Store in the refrigerator for up to 2 weeks.

In a large glass, muddle mint leaves with ginger syrup. Strain into a julep or rocks glass.

Add crushed ice and pour bourbon over the ice. Top with seltzer water to fill the glass. Stir to combine. Garnish with mint and a slice of ginger, as desired.