If I had a daughter, I would name her Sardinia and call her Sardine for short.
Half a dozen sardines
As much garlic as you like
2 medium white onions
The amount of tomatoes it would take to fill your can, I used about 6 different sized romas
These were frozen whole. Defrost. Chop off the heads unless you want them. I slit their bellies and gutted them. Be very very gentle because sardines are extremely delicate fish. The silver skin scrapes easily too. Their bones are thin and once cooked will not do much harm but I was able to pull the entire skeleton out. Try not to damage the flesh so much. You can split them in two fillets or keep them whole.
Half tomatoes and remove the seeds, half them again and again . Roughly cut up garlic and onions.
In sauce pan on medium high heat, drizzle in olive oil. Fry chili flakes, very fragrant. Mine turned a little black there. Throw in vegetables. Stir and break down tomatoes. Put a lid on it for a few minutes, take lid off to stir. Add more olive oil if mixture evaporates and tomato flesh is sticking.
Stir in your sardines, fold gently to incorporate. Cover for a minute.
Off the heat, into your sterilized jar.
Put the jar in boiling water for 10 minutes.
Enjoy! The tomato sauce is great on rice or pasta.