If your plane leaves at 11:00, you'll want to get to Malpensa by 9:00. We had similar timing and opted to spend the night at a B&B in Magenta, located between Milano and Malpensa. For an extra 15 euro, they'll drive you to Malpensa in the morning: http://www.thetravelzine.com/it_w2004_8.htm

Regards, Linda