Using a muddler or the handle of a wooden spoon, mash 7 fresh mint leaves, 1 lemon half, quartered lengthwise, and 1 Tbsp. simple syrup (click for recipe) in a 16-oz. mixing glass or a cocktail shaker 4–5 times just to release juices and oils. Add 1/4 cup bourbon. Transfer to an Old Fashioned glass. Fill halfway with crushed ice, stir, then mound more crushed ice on top. Garnish with mint sprigs.