According to the Food Network, a boxcar is made by mixing lemon juice, Simple Syrup, bourbon and triple sec. It is traditionally served in a sugar-rimmed glass either straight up or on the rocks.
Simple Syrup is made by mixing equal parts of sugar and water and heating while stirring until the sugar dissolves. Begin making the boxcar by stirring together 1 ounce of fresh lemon juice and 1/2 ounce of Simple Syrup in a glass. Pour 1 1/2 ounces of bourbon into a cocktail shaker. Add 1/2 ounce of triple sec and 1 ounce of the lemon juice and Simple Syrup mixture. Shake for 8 to 10 seconds. Moisten the rim of a cocktail glass with a lemon wedge, roll the rim in granulated sugar to coat, and fill with the beverage.