General

Peanut butter and almond milk? Or any other milk than animal milk? Maybe nutella too.

I've just starting drinking gainer shakes and mine are basic, milk and double cream, plenty of calories per glass!

You can always check out the standard milk substitutes like Lactaid or Silk Almond Milk. I can honestly say I have no clue how well they'll work but those are the advertised milk substitutes.

Coconut Milk is the closest to milk texture wise according to google.

same stuff here. for me low-lactose milk works, but not in large volumes. For that purpose no-lactose milk is better, but more expensive.

Previous option I discarded was a soy milk - I just heard when drinking lots of it - it messes up with hormones and estrogen levels are rising. I don't want that personally, but many might want that...

And also I tried almond milk - stuff is just weird... and expensive.