A week ago, baking this year's Leland Awards cake, because I'd pulled up so many crumbs in the frosting on last year's edition, I decided I may as well (1) crumb-coat (something I've literally never bothered with before), and (2) go a little bit looser with the frosting.
And I noticed that where the recipe from the back of the C&H powdered sugar box normally crusts to some extent, my maple-cinnamon variation (farm-bottled Vermont Grade B replacing most of the milk, and ground cinnamon instead of vanilla extract) wasn't crusting at all.
And thinking back, my strawberry variation (with seedless jam replacing, if I remember right, about half the butter and most of the milk) doesn't crust at all, either.
The crumb-coat, and the somewhat looser frosting, did keep me from ripping up the top crust of the cake, but I'm guessing that it would have been more effective (and I'd have been able to go stiffer with the main coat) if it had crusted.
I'm thinking that the syrup in the maple-cinnamon, and the jam in the strawberry, are making those variations hygroscopic.
Is there something I can do to compensate? To encourage crusting?