Chop your onions, leeks and garlic. Put a good dose of olive oil into your pot, add the chopped vegetables and cook but do not brown. Add your chopped bacon and its skin. When these have released their fat, squish the tomatoes in your hands and add them, giving your dish a slight blush. Let all this cook down until you feel that they have really got to know each other, a gentle 25 minutes or so.