Calories dense cat food

[brooksghost]

Our 9 year old Burmese has always been an indoor cat but in the last 6 weeks, we've let him go outside. He's now far more active than ever which has led to him looking quite scrawny.
He's never been a huge eater so I'm looking for something that will help him bring his weight back up.
He's not got a preference for wet or dry food so I'm happy to explore either option plus treats.

I should add- clean bill of health from the vets and up to date with worming.

Google cat recovery food. You can probably get single cans from vets or some pet shops, or order multipacks online.

It's supposed to be palatable so he should eat it. I freeze it in ice cube trays if I don't think I'll get through a whole in a couple of days as it's quite expensive (but I've mainly used it for young kittens, so they were sometimes eating a teaspoon or two at a time).

Renal food adds LOADS of weight. Had to feed it to mine for 3 months for Boycat's CKD, and by the end Girlcat looked like she was going to give birth any second. It wasn't that she liked it so much she was eating more either, still ate the same amount as always.

Within 6 weeks of Boycat being PTS and Girlcat being back on her normal food, she was back to her lean sinuous self.