Frosting for writing on the side of an unfrosted pound cake?

I am baking a pound cake (in a Bundt mold) as my father's birthday cake, specifically a pound cake because pound cakes are among the few cakes customarily served without frosting. (He doesn't particularly like frosting, and given that he's mildly type-2 diabetic, having to monitor his blood sugar and take large, malodorous pills, he's in no hurry to become severely type-2 diabetic, and have to shoot up periodically. While a pound cake has more sugar than most cakes do before frosting, it probably has less than half the sugar of a frosted cake.

So the fact that we have a Bundt pound cake, served unfrosted, is a given.

But I would still like to decorate it: something to the general effect of "HAPPY 77th BIRTHDAY, DAD." But the only available surfaces are, of course, almost vertical.

So I need a very small amount (less than a cup) of frosting that will pass through a writing tip without blowing out the piping bag (I've experienced a blowout), yet won't sag, run, or slump on an unfrosted vertical surface.

As an experiment, I took the heel of a loaf of bread, wrote on it with Cake Mate writing frosting (which they claim sets up dry enough to be used on cookies that can then be stacked), straight from the tube, then propped it up at about the same angle as the side of the cake.

Within a few minutes, it had slumped to the point of being utterly illegible. So much for that idea.

Or I could fall back on factory-made cake lettering. Not that I particularly want to do that.

Is there something that could be made by stiffening up something that already comes in a tube?

Is there something that could be made out of, say, reddi-whip?

Is there something that could be mixed and piped hot, stiffening as it cools to room temperature?

Last night, I picked up a pound of powdered sugar, and this morning, I scaled the frosting recipe on the back of the box to smaller amounts, and also scaled the powdered-sugar-and-water "decorator frosting" recipe in the old Betty Crocker cookbook as well. Tonight, I'll run some tests, and if one of them works, I'll stick the piping bag in the refrigerator for tomorrow night. Hopefully, I'll have something that's stiff enough to hold its shape on a near-vertical surface, but long enough that it can be piped without a blowout.

Side-note: It seems remarkable how so many different frostings can all be called "buttercream," despite huge differences in ingredients, processes, and (presumably) density and handling characteristics. Cf. the cold-process buttercream recipe on the back of the powdered sugar box (I've never even SEEN anybody use an electric mixer for it!), as opposed to the French egg buttercream Alton Brown demonstrates (without calling it anything but "buttercream) on Good Eats, or the Swiss Meringue buttercream I'm told he put in one of his books.

Just read the Wikipedia article. Even more variations.

Kind of makes it hard to talk about it: unless we're specific, it's hard to know what it is we're even talking about.

Well, I just mixed up some very stiff buttercream: 2 oz of powdered sugar, 1 tbsp of room-temperature butter, and 1 tsp of milk. It barely passes through a Wilton #3 tip, and had to be pressed against the test surface (the other heel of the aforementioned loaf of bread) to stick, but so far, it's remaining legible in a nearly vertical position, with no sign of slumping.

I think it ought to work. It's sitting in the refrigerator.

I'll warm it back up when the cake comes out of the oven

The cake is now out of the oven, and the piping bag is almost back up to room temperature. I have a box of blue candles (ones), and a box of white candles (tens). And I found the cache of plastic candleholders.

I remembered to grease the pan, but not to flour it. Fortunately, non-stick coatings have become remarkably effective in recent years; it fell right out.

And it's getting close to dinnertime.

After dinner, the piping bag was back up to room temperature. And so . . .

poundcake.small by Tracker-Backer, on Flickr


poundcake.cut by Tracker-Backer, on Flickr
Maybe a bit dry. But very satisfying.