There's a famous steam locomotive called The Flying Scotsman which I'm sure you can read about elsewhere if you're interested. In 1928 they added a cocktail bar for the first class passengers and this was their eponymous signature cocktail.
To my tastes it does not improve on a Rob Roy but I can see it opening up some non-whisky drinkers (we call them tourists) to our beloved drink.
After researching several versions of this drink online I contacted the national rail museum for the authentic recipe. The proportions they gave me are listed below but they also told me that it was originally made with a single malt (which I don't think is necessary) and was shaken and not stirred (to my horror). No garnish was mentioned but I don't think you can go wrong with an orange twist here.
1 1/2oz Scotch (famous grouse works just fine)
1 1/2oz Sweet Vermouth
2-3 dashes Angostura bitters
1/4 tsp sugar syrup
Orange zest twist (optional)
Add all ingredients to an ice filled mixing glass and stir until chilled and diluted. Strain into a chilled martini glass and run orange zest around the rim before twisting and dropping. If anyone can justify shaking these ingredients please tell me I'm wrong in the comments. Sláinte.