I used a new icing recipe that called for whipping cream. Does it need to be refrigerated because there is cream in it? I have it stored in the fridge now, but what about the cake after it is iced? How long can the cake be left out?

TIA

Is whipping cream the main ingredient in the frosting? Or did you use whipping cream as the liquid in an American b/c?

A stabilized whipped cream frosting is not shelf stable but requires refrigeration except when being served. (Maximum out of refrigerator time is 2 hrs.)

If you can provide the recipe name and/or link to website where you found it, it would be easier to give a definitive response.

Most American b/c's are shelf stable, even when milk or cream are used as the liquid.

Sugar is hygroscopic, or moisture absorbing.
The powdered sugar in American b/c's controls the water activity in the butter/margarine and/or milk or cream in the mixture. (Butter and margarine are both 80% fat and 20% water, while shortening is 100% fat.)

Water activity & microbial growth:
(Prolonging Bakery Product Life.)

http://tinyurl.com/6fbkcz

WJ Scott in 1953 first established that it was water activity, not water content that correlated with bacterial growth:

http://tinyurl.com/bmsato

Formulating for increased shelf life:
(Decreasing water activity results in hostile environment for bacteria.)

http://tinyurl.com/csu2b9

HTH