Marinate the salmon
Halve the salmon, rub well with salt, sugar and pepper and transfer to a deep glass or porcelain container. Arrange the onion rings on top, cover with the thyme and rosemary and pour over the Condimento. The salmon should be completely covered by the vinegar. Press the salmon down with a heavy plate, cover and chill for approx. 24 hrs., turning once.
Remove the salmon and pat dry with kitchen paper. Finely slice and arrange the rosemary and thyme on top.