What to do with a failed cake?

...mix into ice cream...dry in low oven or dehydrator and use as "breadcrumbs"...use as struesel topping on another cake....??

In Denmark (and in other countries around the world), we have this wonderful thing called rum balls. It's basically old cake leftovers mixed with cocoa and, depending on the recipe, something sticky, such as jam. In Denmark, they're usually rolled in sprinkles, shredded coconut or just more cocoa powder if you like a chocolaty taste. They can include rum or rum essence, but don't have to.

I have yet to find a type of cake this doesn't work with. Danish bakers make them from whatever they have laying around at the end of the day, often including danishes and more margerine as the sticky part, and sell them cheaply the next day to students and others.

Slice it and fry it. Then, in the pan, add some sugared milk and let it absorb the milk like in French toasts.

Or just fried, add some maple sirup or custard?

EDIT : @rumtscho is saying that the French toast is a bad option, maybe crumble?

I know you already have an answer you picked and many more good ideas, I would like to add one more to this long list of good ideas. What I do is slice up the cake in pieces about a half inch thick or so, and whether it is a round, square or rectangle cake. I slice the pieces about 2 inches by 3 inches. Then I put them on a cookie sheet on 300 degrees F and cook them until they are nice and dry, it takes about 30 minutes. I would check in 15 minutes to turn over and see how hard they are and even taste them. Put your timer on so you do not forget and you may want to start it at 250 degrees F. Take them out when dried and crispy and let they cool on cookie sheet. Then you can put some powdered sugar or cocoa or not. Believe me when I tell you they disappear so fast on a plate in the kitchen you wonder if you ever made it at all. Good Luck

Slice thin, bake til hard, use as teething biscuits or, if not too hard, cookie type things. I'm going try this with my gingerbread disaster.

I made a nice pudding, by cutting the cake up into small pieces, drying out in a low oven (100 degrees C) for some time, then adding some sliced apple, a sprinkling of cane sugar, and a few knobs of butter. Bake at 175 C. for about an hour. Serve with cream or ice cream.

Have you considered cake pops?

Crumble the cake tto crumb stage, probably best done in a food processor.

Mix with a stiff frosting type binder. I would use a buttercream which would get firm in the fridge.

Incorporate eh crumbs into the frosting. Roll into balls. Roll eh balls in a covering such as sprinkles.

Place on a paper cupcake liner.

Chill.

If you have sticks, stick them in; if not, just eat like the rum ball described above.

Or, use the Momofuko MilkBar recipe for Fruit Loop Meringues using your crumbs instead of crushed Fruit Loop. Here is the link.

http://milkbarstore.com/main/press/recipes-and-how-tos/#Froot%20Loops