Buttercream icing isn't especially difficult to make, but the simplest versions are also the densest. Making a light and fluffy frosting usually involves whipping meringue and boiling sugar syrup, two steps that require time and close attention. When you need a light and fluffy frosting in a hurry, one simple option requires just whipping cream and a box of Jell-o instant pudding. It's ready in just minutes, and it can be eaten almost immediately.
Open the box of pudding and pour the powder into a mixing bowl. Add up to 1/4 of your cream and whisk it vigorously until the pudding powder is well moistened and begins to lose its gritty feel when you rub it between your thumb and forefinger.
Pour the remainder of your cream into the bowl. Affix the bowl to your stand mixer, if applicable, or place the bowl on an unobstructed work space and use a hand mixer or manual whisk.
Whip the cream until it forms stiff peaks. Taste a small quantity of the frosting to judge how well the pudding has dissolved. A slight graininess is acceptable, unless the cake will be eaten immediately, because the powder will continue to absorb moisture from your cream.
Cover your cake or cupcakes immediately, using a spatula or piping bag, before the instant pudding's gums and thickeners "set" the cream to a firm consistency. If eaten immediately, the frosting has a soft, whipped-cream consistency, but if you refrigerate it for 15 to 30 minutes, it will firm to a more frosting-like texture.