There are two main opinions out, if it comes to drinks [not only mixed drinks - but also spirits and other liquors] - the first: you serve it how the guest wants it - the second: you serve it as your standard; assuming you have standards in your bar. There is nothing right or wrong here - there are two philosophies and a lot of grey shades - you just have to understand, what you are doing. Asking the guest for his preferred serve might sound foolish for some guests. Why? Talking of single malt whisky, cognac [and other brandies], but also highballs or just a Martini cocktail: If you are asking, for ice, the guest might assume, that you don't know what you are doing. Brandies and single malt whisky [but also eaux de vie, akvavit, even Irish whiskey] are served by default without ice. Don't argue [or do - in the comment section below], it is just like that. If a guest would like to have it on the rocks, he could ask for it [and in most cases we would be happy to individual...