I reduced the scotch from 2-1/2 to 2 oz to make a more reasonably-sized drink. Robert Hess calls for 1-1/2, but I think that works for a bar where the amount of spirit is controlled. 2-1/2 oz into the mixing glass should be sufficient. I do like the idea of a lemon twist to accent the honey in the Drambuie and a dash of Angostura for complexity.
Dave Stolz's recipe (which is 2 oz Scotch and 1/2 oz Drambuie) calls for including a wide lemon peel and one dash of Angostura bitters. Muddle the lemon zest, Drambuie, and bitters to express the lemon oil. Add a large ice chunk or two to three ice cubes then add the Scotch. Stir briskly to blend and chill.
I like a slightly different ratio of 2 oz blended scotch and 1/2 oz Drambue. Combine in old fashioned glass, add ice, stir.