Martha puts a twist on the classic Kentucky Derby drink by sweetening it with homemade lemon syrup. The bright citrus flavor complements the bourbon and fresh mint beautifully.
Lemon Simple Syrup: Heat sugar, 1 cup water, and lemon zest in a small saucepan over high, stirring occasionally, until sugar dissolves. Remove from heat; let cool 20 minutes. Remove zest; let cool completely. Syrup can be refrigerated up to 1 week. (Makes 1 1/2 cups.)
Cocktail: In the bottom of a julep cup, muddle mint leaves with 1 tablespoon syrup for a few seconds until mint starts to break down. Add bourbon and fill cup with ice; stir until well chilled. Top with more ice and garnish with mint sprig.