Back in the day when i struggled to eat enough calories for optimal gaining when bulking, i used to do a shake in a morning which consisted of:
12 whole large eggs,
2 pints of Whole milk,
6 tablespoons of Nesquik milkshake powder + Few scoops of Protein power if you like to increase protein content.
I used to have one, morning after breakfast, afternoon afterwork/training after my evening meal and last one before bed after late evening snack
The above creates roughly 3 pints of shake containing approximately 2500 calories and nearly 150g protein and contains plenty of mono fats (small amount of sats fats but could live with this) not to mention Calcium, vitamins etc.. Try it, Tastes great and easy to get close to 5000 calories a day as an addition to your standard 3 meals a day and much better than these sugar loaded weight gaining supps.
Brilliant easy solution when your appetite just will not motivate you to eat and as Adam states, much easier to drink than eat, difficult for lots of us to consume the amount of food we require daily for the goals we aim to aquire.