Combine all ingredients in a cocktail shaker with ice. Shake for 20-30 seconds, strain into rocks glasses filled with ice. Garnish with an orange wedge or maraschino cherry if desired.
There are 2 tablespoons in one fluid ounce. If you don't have a cocktail jigger or other way to measure fluid ounces, 3 ounces of bourbon equals 6 tablespoons, 1 ounce of vermouth equals 2 tablespoons, and 1/2 ounce of grenadine is 1 tablespoon.
When scaling up the recipe for a party, know that 4 tbsps = 1/4 cup.