1/2 teaspoon (more or less) kosher salt, or 1/4 teaspoon plain salt
PREPARATION
Put the walnuts in a food processor with the anchovies, water, vinegar and walnut oil. Blend until smooth, stopping a couple times to scrape down the sides of the container with a rubber spatula. With the machine running, slowly drizzle in olive oil.
The puree should be the consistency of a softly whipped cream, not walnut butter. If it seems too thick, add a little more water and pulse or blend until incorporated.
Season to taste with salt. If not using immediately, refrigerate in a covered container.