Skim milk powder?

[emmathomp]

I want to make a cloud cake as a bday present tomorrow. The recipe calls for a tablespoon of powdered skim milk to mix with the whipping cream and sugar. What purpose does this serve? A bag is $3.99 and I don't want to buy it if it's unimortant or can be substituted for something else. Please help! I'm poor!
Thanks!

 

[sparrowgrass]

I bet the powder just helps to stabilize the whipped cream. Hard to tell, though, without the whole recipe.