My latest gainer shake recipe:
-5 oz decaf cold brew coffee
-5 oz lactose free milk
-4 heaping spoonfuls of peanut butter
-4 spoonfuls of chocolate syrup
-4 spoonfuls of lactose free vanilla ice cream
-2 spoonfuls of olive oil
-2 spoonfuls of flax seed
-1 frozen banana
-1 handful of ice
I use a large soup spoon, so this comes out to about ~1600-1800 calories and it's easy to drink, tastes amazing, and it won't wreck your stomach at all.
I can put down two of these a day easily, one before breakfast and one after dinner. Two makes for nearly a full pound of fat worth of calories (3500), mostly in fat and sugar which makes it efficient for your body to store as fat on your body.
Add this to your usual diet, do not meal replace, you still need to eat your BMR calories for the day and you could theoretically gain 1 pound a day as long as you keep it up. I've been doing it for about a week now and I'm seeing those results and it feels sustainable so far.
