Shaving Scuttle
As the years go by and technology advances, it’s natural for objects we once used to become obsolete. This OP thought they were looking at some sort of “weird teacup” and we don’t blame them considering they found it in an old fine China cabinet.
However, this is actually a “shaving scuttle” which was essentially a container to hold hot water while shaving. Now that we’ve moved on to disposable and electric razors, scuttles like this are no longer used. However, we do love the Renaissance feel it has. Speaking of scuttles, there were even coal scuttles that were used to hold coal. Consider that your history lesson for the day.