Mix bourbon and cold mint syrup in a small pitcher. Pack a metal Julep cup with shaved ice, pressing the ice down to compact it. At the rim of the glass, press mint garnish around edges so that it forms a wreath. Add bourbon and mint syrup, dust with a bit of powdered sugar, and drink through a straw cut 1 inch higher than the glass.
To make mint syrup, take the leaves off of 4 sprigs of mint, place in a small bowl, and pour 1 cup of 2:1 simple syrup over the leaves. Let steep for 15 minutes, strain the syrup, and chill. Obviously, high quality Bourbon is the way to go here. Pappy 15, George T Stagg, pick something nice.