Ignite 1 rosemary sprig, carefully allow it to burn slightly then extinguish flames. Invert a glass on a heatproof work surface and immediately place smoking rosemary under the glass and allow it to smolder.
Meanwhile, pour whiskey, vermouth and both bitters over ice in another glass and stir to combine and chill liquids. Alternatively, this mixture can be shaken in a cocktail shaker that’s been filled halfway with ice.