Step by step

Brown the onion in butter

Tips
Keep a little parsley plant on your balcony which will come in handy when you need to add a bit of freshness and flavour to your dishes, whether meat or fish.
Trivia
The original recipe does not require the addition of fresh tomatoes nor tomato passata or even tomato paste. This addition took place in modern times to give more creaminess to the sauce and a touch of freshness.