Blended Scotch, sweet vermouth, and Angostura bitters — a Manhattan made with Scotch, and it's a revelation.
The Rob Roy was created at the Waldorf-Astoria Hotel in New York City in 1894 to celebrate the opening of a Broadway operetta about the Scottish folk hero Robert Roy MacGregor. It's structurally identical to a Manhattan (whiskey, sweet vermouth, bitters) with Scotch whisky in place of American whiskey.
The substitution changes the drink's character significantly. Where a Manhattan has the clean caramel-vanilla sweetness of American bourbon or the pepper of rye, the Rob Roy has the earthiness, dried-fruit complexity, and sometimes smokiness of Scotch. A blended Scotch works well; a lightly peated expression (Monkey Shoulder, Dewar's 12) adds complexity without overwhelming the vermouth.
Replace sweet vermouth with dry vermouth. A drier, more delicate drink that showcases the Scotch more.
Use ½ oz each of sweet and dry vermouth. Between the standard and dry versions.
Use a lightly peated single malt (Bowmore 12, Ledaig 10) instead of a blended Scotch. The smoke and vermouth create something complex and unexpected.