-
1
Warm the olive oil in a wide, heavy-based pan over low-medium heat. Add the sliced onion and the whole garlic clove. Cook gently, stirring occasionally, until the onion is translucent and soft but not coloured — 8 to 10 minutes. The onion must show no resistance when pressed against the pan.
-
2
Add the yellow and red pepper strips and the chopped tomato. Stir to coat in the oil. Cover with a lid and cook over low-medium heat for 45 minutes, stirring every 10 minutes, until the peppers have lost all resistance and the mass is soft, jammy, and beginning to collapse. This is where the dish lives or dies: insufficient cooking leaves a raw pepper bite that no amount of rest will correct — press a strip against the side of the pan; it must offer no resistance whatsoever.
-
3
Remove the pan from the heat entirely. Lay the anchovy fillets across the surface of the peppers. Allow the residual heat to melt them, folding gently once or twice until no fillet remains visible and the anchovy has dissolved into the mass — 2 to 3 minutes. The smell should be savoury and sweet, with no sharp fish note.
-
4
Add the white wine vinegar. Stir once to distribute. Remove and discard the garlic clove. Taste: the vinegar should register as a clean brightness cutting the oil richness, not as acidity. Season with salt only if needed, remembering the anchovy has already salted the dish.
-
5
Transfer to a ceramic or glass vessel. Allow to cool to room temperature uncovered, then cover and refrigerate for a minimum of 12 hours before serving. The surface should show a thin film of settled oil and the colour will have deepened to a burnished amber-red. Serve cold or at room temperature.