Considered by many to be the Basque national sauce whether it’s used in risotto, a vinaigrette or squid in their own ink.
5 Spanish onions, halved and thinly sliced
1 green bell pepper, seeded and cut into small dice
1½ tablespoons extra-virgin olive oil
2 cups water
½ cup canned whole plum tomatoes, crushed by hand
1½ tablespoons squid ink
Pinch of sugar
In a heavy saucepan, combine the onions, bell pepper, oil, and a little salt, cover, place over medium-low heat, and sweat the onions, stirring occasionally until the onions are soft and melty but not caramelized beyond a light blond. Raise the heat to medium, add the tomatoes, then bring to a boil and cook for about 5 minutes, until the tomato has lost some of its acidity.
Turn down the heat to a simmer and add the squid ink, cooking for a couple of minutes. Add the water and continue to cook for about 30 minutes, stirring occasionally, until the onions and pepper have almost entirely melted out and the sauce is sweet and complex.
Taste the sauce and adjust the salt. The sauce should have a very light hint of sweetness, so add sugar only if necessary. Blend in a blender until completely smooth. Use immediately or freeze for up to 3 months.