my husband's favourite donut (and I mean favourite - last week they appeared
to be out and he sent the little worker-fellow searching for more "in the back") is a Boston cream. It's got custard injected, instead of jam

The few Scots on this board (and jmh, of course) will be salivating when I mention the word fudgies. They are very like what you have described here, Bean, but absolutely delicious. Substitute fudge for the custard....... Yum!