I know exactly what you mean about the tortoiseshell/food thing...a little one came to my garden a few years ago, she was a stray and stayed but was incredible fussy about what she was fed, would go hungry rather than eat things like Felix or Whiskas. I used to give her Smudge from Dunnes. It's v cheap, 2.90 for 6 cans and she loved it. She thrived on it too so my snobbishness about it being so cheap was proved wrong! I'm convinced your cat will love it, it's very gravy-ish.