Many cooks seriously underestimate the value of the onion, often because they don't know how to prepare them properly. Caramelized, these humble ingredients develop a rich flavour which can magically enhance any savoury dish.

We all immediately think of sugar when we see the word caramel - and you'll see some experienced chefs adding sugar when preparing onions. But in fact, caramelized onions are simply onions that have been cooked long enough for their own sugars to emerge and caramelize.

You can vary the amount of sweetness by your choice of onions. Mild onions will cook sweeter than stronger ones, and flatter onions tend to be sweeter than round ones – don’t ask me why!

If you're planning to caramelize onions, set aside some time - because caramelizing onions need watching. There’s a very fine line between beautiful, caramel-coloured onions and burnt offerings!

You can achieve nice, pale gold onions in about 10 minutes, but if you want a rich, deep gold, It can take 30-40 minutes. It's tempting to walk away, but please don’t - you’ll need to toss them every 5 or 10 minutes to stop the bottom pieces burning, and be ready to snatch them off the heat as soon as they’re ready.

If all that sounds too much like hard work, you can speed up the process by putting the onion in the microwave for 5 minutes before you start.

But I’m getting ahead of myself – let’s look at how you cook onions from the beginning, whether you want to caramelize them or not:

• Slice or chop your onion, depending on what you need for your recipe. Be generous – onion shrinks a lot as you cook it.

• Heat some oil in a good heavy pan. What kind of oil is up to you – I like rice bran oil, because it has no flavour of its own, so it lets the sweetness of the onion shine through.
• Please don’t put the onion into the pan until the oil is hot – that way lies soggy onion! If you’re not sure, sacrifice a test piece. If it sizzles, it’s hot enough.
• Tip all the onion into the pan and mix until it is well coated with oil. Turn down the heat, sprinkle with salt and mix again (the salt draws the flavour out of the onion).

Now simply let the onion cook gently, turning occasionally to make sure it doesn’t stick.

For most recipes, cook the onion until it’s really soft, but before it starts to turn brown. If the recipe calls for caramelized onions, or if you want them for garnish, just keep going until it develops that rich caramel colour.

I’m one of those people who used to cook my onion for a few minutes before throwing in the rest of my ingredients. Now, I start my onions 10 or 15 minutes before I begin preparing the rest of the recipe. The difference in flavour in my pasta sauces is astonishing!

This is a good stand-by if you can't get to the shops. The aroma and taste of the slow-cooked onions will transform the other basic pantry ingredients! But be warned - though this is easy, it’s not quick. Make sure you cook the onions long enough, and then be patient while the tomatoes cook down to a rich, thick sauce.

You can use fresh tomatoes if you have over-ripe ones to use up (Roma are the best), however unless you're prepared to cook the sauce for a very long time, you're going to have to skin the tomatoes first - which I never have the patience to do!

• Olive oil
• 1 large onion
• 1 can Italian tomatoes
• Squeeze of garlic paste (or equivalent), if you have it
• Your choice of Italian herbs - dried, fresh or paste, whatever you have
• Chicken stock - cube, 1 tsp powder or fresh

Slice the onion. If you're not an onion fan, chop it finely (it will disappear in the sauce).

Cook the onion as directed above - don't forget to add the salt! Don't over-caramelize - when the onion is soft and buttery, add the garlic paste and stir for a few minutes.

Add the whole can of tomatoes, juice and all, and the herbs. Crumble in the stock cube or pour in the stock, and stir well.

Bring to the boil then reduce the heat and simmer, uncovered, until the sauce is thick. This can take anything up to 40 minutes - even longer if you have used fresh stock because of the extra liquid.

This is the basic tomato sauce. I often cook some chorizo or Italian sausages, chop them up and add them to the sauce just before serving. If you'd like to add mushrooms, add them towards the end of the cooking or they'll disappear! For bolognese, brown some minced beef and add in when you add the tomatoes.

Buon appetito!

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All text copyright Marisa Wright.

Onion photo courtesy of ApolloJack on Flickr. Sauce photo from Wordridden, also on Flickr.