A vote for SquawI've had the luxury to ski Europe and US resorts. I'd observe that most, not all, areas have some level of expert terrain. Some resorts market their expert reputation and so attract the weekend (or week) warriors to test themselves.
So the resorts with an expert attraction are the Altas, Jackson Holes, Squaws, Whistlers ... of this world. Or actually of this continent as it seems that the European resorts, let alone Asian ..., don't seem to get many votes. Except by folks who have skied there and are terrified in having to jump crevaces on a marked trail or dropped down the face of a glacier to get back to the resorts. So I'd suggest that Chamonix and Saint Anton are other areas with an expert reputation. Meanwhile there are runs like Jockeys in Courcheval that are miles (or kilometers) long expert runs which are suitably challenging given the changeable snow conditions if nothing else. Or the off-trail stuff between Tignes and Val d'Isere, or the unserviced valley in Les Trois Valleys, or the frequent 'watering' holes at any Austrain ski area, or ....
And snow conditions make a difference - I was at some stupid little hill in the Pokonos and scared myself silly on what they laughingly called snow.
But Squaw Valley has a book, Squallywood, about some of the terrain that highlights lines that no sensible weekend warrior, British or otherwise, would attempt. And it doesn't include all the available lines - Shirley Canyon for example. It rates the lines based on such things as visibility and difficulty and even recognizes that taking them on a monoski deserves extra recognition. Nor does the book lower itself to recognizing the mainstream expert terrain like KT22, Broken Arrow, Headwall, ... Remember at Squaw they mark the lifts, not the runs, for challenges to be expected.