Gaining

Helping my boyfriend get chunky

My boyfriend recently told me that he is ok with me fattening him up a bit. When we met last summer he was 40lbs lighter than he is now. He is very muscular however. I specifically want to see his belly gain at least 15lbs more fat. How do I do this the “right” way? I don’t want him to have any health issues, he does work out every day and has been taking mass gainer. Is the easiest way to do this to have him drink heavy cream? What dinners can I make him to help with this?
3 years