Cool It

• Most types of icings, including royal icing and buttercream, can safely be stored at room temperature. A whipped cream frosting is one of the few exceptions. Whipped cream is highly perishable and leaving a sheet cake out that's been frosted with it is a recipe for potential food poisoning disaster. Sheet cakes frosted with whipped cream must be stored in the refrigerator at a temperature of 40 degrees Fahrenheit. At this temperature, bacterial growth is slowed. The cake is safe for up to three days. You can freeze whipped cream for up to two weeks, according to the Colorado State University Extension, but the quality of the cake may suffer.

Pretty It Up

• Don't just toss the sheet cake in the fridge, though. Wait until the cake has completely cooled before you frost it with the whipped cream. At this point, insert two or three toothpicks in the top of the cake. Lay a few sheets of plastic wrap over the cake. The toothpicks will hold the plastic wrap up so it doesn't stick directly to the cake, creating a gooey mess.

Make It Last

• When you first whip whipping cream, it develops soft, fluffy peaks and a creamy texture. Put it in the fridge for a day or two, though, and it deflates and can even become watery. This is the last thing you want to happen to your frosted sheet cake. Professional bakers solve this problem by adding softened gelatin to the whipping cream. The gelatin adds structure so the whipped cream stays firmer, longer. To make stabilized whipped cream, soften unflavored gelatin in a bit of cold water. Add a little boiling water. Whip the cream until it forms soft peaks. Add a bit of warm cream to the warm gelatin and add this mixture to the whipping cream. Whip for a few more minutes until you get stiff peaks.

Wait Until the Last Minute

• Refrigerating leftover cake made with a whipped cream frosting is a no-brainer. You must keep it cold to keep it safe. On the other hand, there's no reason why you need to frost a sheet cake with whipped cream ahead of time. Even when you're using a stabilized whipped cream, the quality begins to deteriorate after only 24 hours. For the freshest whipped cream cake, make the sheet cake one or two days ahead of time and wrap it in plastic wrap. Store it at room temperature. Make the whipped cream right before you serve the cake. It only takes five minutes or so and the cake will be perfectly light, creamy and delicious.