Warm two silver vessels (with insulated handles) with hot water. Leave 1.5 ounces of hot water in one and pour the scotch into the other. After warming the scotch, ignite it with a match. Pour the flaming scotch into the other vessel containing the hot water. Pour the flaming liquid back and forth a few times. Have a London dock glass prepared with lemon juice and Simple Syrup, and pour the flaming mixture into the glass. Garnish with the twist of lemon. Note: The scotch will not ignite unless it is succiently heated. Try warming it gently for less than a minute in a saucepan over a low flame.
Jerry Thomas's famous flaming drink is challenging and can be dangerous. Use large mugs with insulated handles and try pouring back and forth a few times with water to practice. Use mugs that are designed for hot liquids. If they are glass, look for the "T" on the bottom that indicates the glass is tempered. Finally, make a small amount for each batch to avoid spillage. And try it outdoors to avoid a chance of fire. Indoors, make it over a nonflammable surface. Never attempt it at table.