I have made the same fudge frosting 5 times now, but for some reason the last time I made it the frosting never firmed up; it never got solid enough to spread. As far as I know I made it the same as always but, based on the runny results, clearly I didn't. I gave up and made something else for the cake in question, and just frosted a plain cake at home w/it today (because really, why waste chocolate?!). It is so runny that the top layer of the 8" half-cake--which hasn't been moved--slid 1/2"! I didn't need to ice the sides because the frosting just oozed down from the top. No, it isn't a ganache! This frosting has never required refrigeration to maintain its consistency. I used the same stuff on my fish cake w/no problems.
What might I have done wrong to get that kind of result with a frosting, and how might I have fixed it? Is it as simple as adding more p. sugar? I was worried that once it had totally cooled, it would be far too late to do add sugar, since adding it while the chocolate was warmed did a good job of dissolving it. Plus it is plenty sweet enough, even in its runny state.
Here's the recipe in case it helps anyone to figure out what might have gone wrong:
Fudge Frosting
3/4 cup (1 1/2 sticks) unsalted butter
3/4 cup sugar
3/4 cup half and half
6 ounces unsweetened chocolate, chopped
4 ounces semisweet chocolate, chopped
1 teaspoon vanilla extract
2 1/2 cups powdered sugar
1/4 teaspoons ground cinnamon
Combine butter, 3/4 cup sugar, half and half in large saucepan. Stir over medium heat until sugar dissolves and mixture simmers. Remove from heat. Add both chocolates; whisk until smooth. Whisk in vanilla. Pour chocolate mixture into large bowl. Sift in powdered sugar and cinnamon; whisk to blend. Press plastic onto surface of frosting. Chill just until firm enough to spread, stirring occasionally, about 1 1/2 hours.
Thanks!
Thanks! Actually it doesn't get hard even in the fridge, although it does get a little less liquid. You can spread it straight out of the fridge, it's still so gooey. But then at room temp it turns to glop. What does that usually mean?? The temp in my kitchen is about 70 degrees.
Of course I can just keep the cake in the fridge since I'm just eating it at home, but I really want to figure out what went wrong so that it doesn't happen again, since it was MEANT to go on a decorated cake. I've used it successfully before, so I know that this is not just the way the frosting is meant to be. I know I did something wrong, but I don't know enough about cake "chemistry" to know what to watch for next time. Overcooking the butter/cream? Undercooking it?? Undermeasured an ingredient in the cooked part? Messed up on the powdered sugar? Etc.
Help!
Is it extra humid in your area right now? Maybe you need to cut down on a liquid in the frosting if it is? Just a suggestion don't know if it would help or not.
Hi, thanks for your suggestion! I wonder if cutting down on the liquid would work. My first instinct was that maybe I didn't measure the p. sugar well, but I felt it was too late to add more as I think it would be gritty if added at this late stage.
Still, I don't think it's the humidity, because it doesn't even get hard in the fridge! It's driving me crazy! I need a frosting doctor or technician, or perhaps a chemist or physicist, to help me figure out this mystery! 
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