Slice a lemon in half and then cut one thin round slice for garnish.
Grill lemon halves flesh side down for 2-3 minutes until lemon develops nice char and is warmed throughout. For the garnish slice, grill on both sides until you see those captivating grill marks. Keep an eye on them to prevent over-charring.
Juice the grilled lemon halves, it should produce 1 oz of juice.
In a shaker filled with ice combine whiskey, lemon juice and simple sugar.