Pesto alla genovese

Seven ingredients, no cooking, and one piece of equipment that genuinely changes the result. Pesto is basil, pine nuts, garlic, two cheeses, salt and olive oil, worked to a paste in a marble mortar with a wooden pestle.

You can make it in a food processor and it will be pleasant. It will also be darker, sharper and slightly bitter, and once you have tasted the two side by side the reason for the mortar stops being romantic.

Ingredients

Enough for 500 g of pasta, serving 4.

	Metric	Imperial
Basil leaves, small and young	50 g	1.75 oz
Pine nuts	15 g	0.5 oz
Garlic	1 clove	1 clove
Parmigiano reggiano, grated	45 g	1.6 oz
Pecorino sardo, grated	20 g	0.75 oz
Coarse sea salt	a good pinch	a good pinch
Ligurian olive oil, mild	70 ml	2.4 fl oz

The basil should be small-leaved and young. Large mature leaves carry a mint-like note that turns the pesto medicinal, which is the single most common reason a home batch tastes wrong. Genovese basil is grown for this and is picked young for the same reason.

Both cheeses matter. Parmigiano brings the sweetness, pecorino sardo the salt and the edge, and one alone leaves an obvious hole.

Never wash the basil under the tap and never bruise it. Wipe the leaves with a cloth if they need it.

Method

1. Crush the garlic and the coarse salt together in the mortar until they are a smooth paste. The salt is doing the cutting.
2. Add the pine nuts and work them in until the paste is even.
3. Add the basil a handful at a time, with a little more coarse salt, and work it against the wall of the mortar with a rotating motion. Do not pound. You are grinding the leaf open rather than hitting it.
4. When the basil has become a bright green cream, work in the two cheeses.
5. Pour in the oil slowly, stirring rather than grinding, until it is a loose spoonable paste.
6. Use it cold. It never goes near heat.

What goes wrong

It is dark green or brown. Oxidation, from a blade or from pounding. Bruised basil browns within minutes and no amount of oil on top will bring the colour back.

It is bitter. Overworked basil, mature leaves, or a strong peppery olive oil. Liguria uses a mild oil precisely because a Tuscan one would fight the basil.

It is sharp and harsh. Too much garlic, which is the easiest mistake to make because one clove looks like almost nothing in the mortar and is correct.

It seizes on the pasta. Heat. Loosen it with a spoonful of the pasta water off the flame and never return the pan to the hob.

Why it works

A blade cuts basil cells and spins fast enough to warm them, and both release the enzymes that oxidise the leaf. A pestle grinds the cells open slowly against stone at room temperature, which ruptures them without the heat, so far less of that reaction happens and the chlorophyll stays green.

The marble matters for the same reason: it is cool, heavy and slightly rough, so it does the work without the friction a metal bowl would generate.

At the table

Pesto is a sauce rather than a course, and in Liguria it goes on trofie, trenette or linguine. The classic dish is trofie al pesto with potatoes and green beans boiled in the same water as the pasta, which sounds like too much and is the version worth making once. The starch from the potato helps the sauce cling.

It also goes into minestrone, spooned in at the table rather than cooked in the pot, which turns it into the Genoese version of the soup.

There is a world championship, held in Genoa, contested in marble mortars, and it is taken seriously by people who have grown up doing this.

Jarred pesto is a normal thing to buy and nobody is snobbish about it on a Tuesday. It is also a different product: it is pasteurised, which is why it is darker and why it keeps.

Never serve it hot, never bake it, and do not put it on bread as a dip. Liguria puts pesto on pasta and on soup.

What an Italian would say

That the mortar is not nostalgia and that you can taste the difference. That the basil has to be young. And that the cheeses are two, which is the detail most recipes outside Italy quietly drop.