How do you make a tomato sauce taste less flat?

"Flat" is the most useful complaint in the kitchen, because it is specific. The sauce is not wrong, it just isn't saying anything. That is a balance problem, and balance problems have a short list of suspects. We go through them in order, one change at a time, tasting in between, because two fixes at once means you never learn which one did the work.

1. Salt, before anything else

Most flat sauces are under-salted, full stop. At the right level, salt doesn't make a sauce taste salty; it makes the tomatoes taste more like themselves. Add a small pinch, stir, give it a few seconds, taste. Repeat until the sauce suddenly seems brighter and rounder. The moment it tips into tasting salty, you have gone a pinch too far, so go slowly near the end.

One caveat: if the sauce is going onto pasta cooked in properly salted water, or getting a snowfall of Parmesan, leave it a touch under. The plate will finish the job. (How much is enough is its own question: /food/how-much-salt/.)

2. Fat, the thing that makes it feel finished

A sauce made with a timid splash of oil tastes thin even when it is well seasoned. Fat is what makes it feel complete in the mouth. Two routes:

• Butter, stirred in at the end off the heat, softens sharp edges and makes the sauce feel plush.
• Raw olive oil, a thread over the finished sauce, adds a green, peppery top note that the cooking oil has long since lost. More on that in /food/finishing-with-olive-oil/.

3. Acid or sweetness: which way is it leaning?

Now taste honestly. Is the sauce dull and heavy, or sharp and thin?

• Dull and heavy wants brightness: a small squeeze of lemon, a few drops of red wine vinegar, or a splash of whatever wine is open. Add a little. Acid is easy to add and impossible to take back.
• Sharp, tinny, a bit sour wants rounding. Butter often handles this alone. Otherwise a longer simmer, a grated carrot cooked in at the start next time, or a small pinch of sugar. No shame in the sugar. Tomatoes vary from tin to tin and month to month; a pinch is a correction, not a confession.

4. Time, gently

A sauce cooked briefly can taste raw and watery. One that has simmered until it has thickened, darkened slightly and the oil starts to gather in little pools at the edge has concentrated. That glossy, slightly separated look is the cue. Keep the heat low and stir now and then so the bottom doesn't catch.

The exception: some sauces are meant to be quick and fresh. If you wanted bright and summery, don't simmer it into jam.

5. Depth, if it still needs it

Seasoned, rich, balanced and still a little one-note? It is missing depth. What we reach for:

• A spoonful of tomato paste fried in the oil until it turns brick-red, before the tomatoes go in.
• A Parmesan rind dropped in to simmer, fished out before the sauce goes to the table.
• Onion, or a proper soffritto, cooked slowly at the start (see /food/what-is-a-soffritto/).
• Garlic taken to pale gold, never brown.
• A pinch of chilli, not for heat but for lift.

For more ways to build savoury depth, /food/umami-without-meat/ goes further.

What not to do

Don't throw five things in at once. Don't add dried herbs at the very end, where they taste dusty; they want time in the pot. And don't judge the sauce from the spoon alone: taste it on a piece of pasta or bread, because that is how it will be eaten.