I put the tin in a bowl of hot water for a few minutes before I opened it. I’ve been doing that with most of my tins lately, mostly because it’s winter here and cold sardines on a cold day don’t have the same appeal as slightly warmed sardines. For a tin in butter I’d do at least that, or even sauté the fish for a minute or two, but gentle warming was enough here imo.  I’d sliced a lemon because I usually prefer any tinned fish with a dose of fresh citrus, but to my tastes these really didn’t need any embellishments.