Fastest way to gain weight?

Ok, I eat all the time, pretty much, and fatty foods like bacon and eggs, pizza, ice cream etc. sometimes I'll drink Ensure 'for gaining and maintaining healthy weight' and I just cant ever seem to gain or maintain anything. I'm not complaining about having a small/skinny figure because I'm happy that Ive never struggled w/ diets etc. but its not just skinny, I think I look malnourished. So I would like to know what will help me Quickly gain weight- I'd like more overall and especially on my face- preferably my too if threres certain exercises that helps for that.. thank you