Sable is (AFAIK) a very specific type of shortcrust pastry, so shortcrust should be fine if it doesn't already exist - that's a pretty well-known baking term, at least in North America.
On the other hand, low-frequency tags are automatically purged from the system, so it's probably a lot of effort for nothing. Any one of those tags you create will probably disappear very soon. I'd just slap a dough or pastry on it and be done with it. If we somehow end up getting a ton of questions about sable or shortcrust within the next year, we can manually retag or add a tag at that point.
IMO, at this point in our site's lifetime, that's more or less how all new tags should be getting created, i.e. finding something important in common between a bunch of pre-existing questions and then adding the tag when it actually has value. Maybe on sites like Stack Overflow it makes sense to create new tags as one-offs because new technologies are constantly being developed and it'll probably get used again. But with cooking, the landscape doesn't change that much or that often; if a tag doesn't already exist yet, it's because it's a subject that's almost never discussed on the site, and probably isn't worth creating a tag for until it's more popular.