Fill a mixing glass two-thirds full with ice cubes.
Add the Scotch whisky, sweet vermouth, and dry vermouth.
Add the Angostura bitters.
Stir steadily for 25–30 seconds until well chilled and properly diluted.
Strain into a chilled cocktail glass.
Optionally express a lemon twist over the surface, then discard, and serve.
Using a blended Scotch keeps the whisky from overpowering the vermouth balance, but a lightly peated single malt adds welcome complexity; avoid heavily sherried expressions, which can clash with the dry vermouth.
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