It's not easy, or rather it's not something you think about very much, but it's a shame to throw away the oil used to preserve tuna or tomatoes, because it's naturally perfumed with whatever's been preserved in it.
And this taste, these aromas, will then be transmitted to your future preparations.
To take the example of the tuna in oil and the
vinaigrette sauce for the salad, you proceed as usual for your salad, but when you add the tuna you collect the oil in a bowl or small jar.
Add vinegar, mustard, salt and pepper, mix well and your tuna-flavoured dressing is ready.
Just about anything that can be preserved in oil (fish, vegetables, cheese, etc.) can be used in this way, not just in a sauce, but as a cooking fat, for example.
Grill tomatoes in a little rosemary oil with cubes of feta cheese, for example, and you'll be amazed at the results.
So far, we've only talked about oil, but this applies to virtually all preservative fats.
In the same spirit, another example: roast potatoes in a little
rillettes fat, and enjoy the resulting taste, in addition to the crispness of the roasted potatoes.
To sum up: don't necessarily throw away the fat used to preserve your food - it can often be used to accompany a recipe, or in cooking.