There is an important distinction to be made between a Rob Roy and a Manhattan, and there seems to be some confusion going on here. A Rob Roy is scotch (best if it's blended, some of the peaty and smoky flavors of single malts will taste weird in cocktails) combined with both sweet and dry vermouth, as well as bitters (I like Angostura, but a lot of people also go with Campari). Combine in a shaker with ice, shake (duh), and pour into a chilled martini glass. Serve neat with a maraschino cherry (get the pre-booze soaked cherries if you're awesome).