Among the San Sebastian locals, it's known as "the holy trinity" – three dishes cooked so perfectly, prepared so lovingly, that they alone can sustain one of a city's most cherished restaurants. And the truth is that it's just three simple ingredients that make Bar Nestor what it is today.
Here comes the first one. A barman pushes his way through the lunchtime crowd and drops a large plate in front of me.
It's covered in chunks of tomato – fresh "corazon de buey", or ox heart tomatoes – that have been splashed with rich olive oil and a little white wine vinegar, doused liberally with salt, and served with hunks of crusty bread.
This is the first of Nestor's trinity: tomato salad. And it's delicious. Almost unreasonably delicious. Plain old hunks of tomato shouldn't be able to taste this good. But they do, and it's not long before my partner and I are mopping up the juices with bread and looking around for any signs of dish No. 2.
All around us this little bar, set in the old town of San Sebastian, high up in Spain's Basque country, is heaving with a solid lunchtime crowd, people desperate to get their hands on the city's best cuisine. The walls here are covered in testaments to Nestor's popularity, football jerseys signed by local stars who've eaten here, a signed cycling jersey, and, in a sign of the reverence with which food is held, a framed chef's coat adorned with the autograph of a local gastronomic star.
Today Tito, brother of Nestor, straight-faced and gruff as ever, is standing behind the bar taking orders, pouring glasses of txakoli, the Basque sparkling wine, yelling orders to the kitchen and finding tables for the guests. It's a chaotic scene, but warm, friendly.
Bar Nestor is a local institution. How does a restaurant stand out in San Sebastian, you might wonder, in a town completely obsessed with cuisine, in a town with more Michelin stars per capita than any other, in a place in which even the smallest bar is experimenting with molecular gastronomy, where everyone is turning out innovative, world-class cuisine?
You keep things simple. You go back to basics.
That's what Bar Nestor is all about: simple, traditional Basque food done extremely well. There are no tricks. No gastronomic sleights of hand. There's not even a menu. Just the holy trinity. Well, the holy trinity plus one.
Most bars in San Sebastian, you soon discover, have a single specialty, one dish they're known for. At Goiz Argi, a few doors down, it's prawn skewers served with tangy vinaigrette. At La Vina, just around the corner, it's cheesecake.
At Bar Nestor, however, there are four: the holy trinity, plus one that rarely makes an appearance at all, the tortilla.
Nestor and his wife only make two of their famed Spanish omelettes each day – one for lunch, and one for dinner. Each tortilla is divided into 12 serves, and once they're gone, they're gone. You can find people hanging around outside the bar about an hour before it opens, desperate to get their name on the list to secure a slice.
I missed out today, which is why I'm sticking to the holy trinity. Soon, I can see another barman pushing through the crowd with dish No. 2: fried padron peppers. These large green chillis have been flash-fried in a hot pan with a little olive oil, doused (liberally, of course) with salt, and thrown on a plate. Done.
This food here is so simple, so plain, so different to the innovative cuisine served everywhere else in town, and it's delicious. The padron peppers are a little spicy, a little salty, and heavy on their own flavour. Nestor's thinking, obviously, is that if you're going to eat padron peppers, you want them to taste like padron peppers.
And now here comes the final point in the Nestor triangle, another local specialty, another simple dish that's the crowning glory of all that's good in the world at this very point in time: the txuleta.
A txuleta is a Basque cut of beef so big that it could have been hacked off a dinosaur. It's a sirloin on the bone, a good kilo of meat, a steak that's been cooked slowly over hot coals before being sliced, then doused with salt, and served. No accompaniments. No side dishes. Just an enormous slab of juicy, salty, perfectly cooked meat.
And pretty soon it's merely a dirty plate, a blackened bone and a few knives and forks. It's the end of the holy trinity. And it's heaven.
Bar Nestor is in San Sebastian's old town, at Calle Pescaderia 11. It opens at noon and at 7pm, with a small break for siesta in between. See www.barnestor.com.