Gaining

Slow and steady wins the race, as they say :-) Pizza, pasta and ice cream should do the trick!

Maybe look into something like heavy cream?

Try mixing/cooking it with something.

I found Double Cream tasted ok when made with ice cream milkshakes.

The only time I had any issues was when I tried mixing it into a non-ice cream milkshake using "Crusha", I suspect the Ice Cream eases digestion.

For me, heavy cream gives me a lot of gas and I burp all the time. So I will try the ice cream.

Heavy cream works well for faster gaining because it has a high fat content and some people find it easy to consume. If you're someone that struggles with drinking cream you can try cooking with it or you can try adding other high fat content foods to your cooking and diet.

Peanut butter, olive oil, coconut oil, butter etc. are all high in fat and can be easily added to foods you enjoy. Just be sure to add oils and butter to foods and don't drink them on their own, otherwise you're going to find your digestive system riddled with grief. Eat with carbs ideally to help your guts handle it.

Forgot to add.

The way I did it is as follows:
1) Add a drop of milk
2) Add the Ice cream
3) Wait a few minutes for it to soften
4) Blend
5) Add Cream
6) Quick blend again

The reason for adding the cream later is to reduce lumps.