I usually use it for Pascha, which is a Russian Easter traditional cheesecake-like dish. Since a single recipe calls for 1 1/2 lbs of powdered sugar, 2# would be pretty easy (but it makes almost 10# of cheesecake).
Honestly though, pantry challenge or no, I'd set aside the powdered sugar... trying to find a way to use up 2# of sugar seems like a fairly unhealthy thing to do to me. Use it up 1/2 c at a time - it's far more reasonable, and it will go further, too. Or like a pp said, use it in recipes that call for regular sugar as you go about your routine cooking.