I've done a Google search and I am seeing different answers. While all agree on what it actually is, that being "the upper layer of milk in a container enriched by whatever cream has risen" and that it occurs in non-pasteurized milk.
What everyone disagrees on is today's equivalent. The following summarizes the answers, which pretty much leaves it wide open.
- It is heavy cream.
- It is light cream.
- It is half and half.
- It is evaporated milk, undiluted.
- It is evaporated milk, slightly diluted.
You can see my problem here.
I cannot figure out what is really the equivalent of today. If I had to make my own best guess, I'd go with #1. In fact, I listed them precisely in the order which I would imagine it goes from most likely to least likely. Clearly evaporated milk is NOT top milk. It may be passable as a sub, but is not the actual thing.
So! Does anyone have a definitive answer?