For the Sour Mix: Stir together the lemon juice and Simple Syrup in a glass.
For the Boxcar: Pour the bourbon into a cocktail shaker. Add the triple sec and 1 ounce of the sour mix. Shake for 8 to 10 seconds. Wet the rim of a cocktail glass by rubbing it with the lemon wedge. Roll the rim of the glass in sugar to coat. Strain the shaker into the sugar-rimmed glass. This cocktail can be served straight up or on the rocks.
Put the sugar and water in a small saucepan. Cook over low heat, stirring, until the sugar dissolves. (Alternatively, heat in the microwave.) Store in a sealed container in the refrigerator.