I wanted to post this because I am bulking and for some reason never thought about doing this over the past 3 years of lifting. This should be used as a supplement to a bulking diet. It should by no means be included in a "clean" bulk diet, but does offer a ton of calories, comparable to a store bought weight gainer.
Throw all into a blender with a couple ice cubes:
8oz 2% or whole milk (~140 cals)
1/2 cup oats (~140 cals)
1 banana (~150 cals) <--- correct me if this is off
2 tbs natural peanut butter (~200 cals)
50g Whey protein (~250 cals)
-----------------------------
880 cals
*** IMO this is healthier than the stuff you buy, BUT still not good for any real diet because you are mixing ALOT of carbs and fats.