Rinse OF glass with Scotch. Stir remaining ingredients with ice in a mixing glass, strain, serve over one large cube. Garnish with lemon twist.
Though just a rinse, the Islay Scotch plays an important role. I used vanilla-infused maple syrup, but any grade A medium amber syrup should do the trick. Bitter Frost is a rye-based, sarsaparilla-dominant bitters.