MAKES: About 1 quart

TIME: 26 hours, largely unattended

Mushroom ketchup has been made in England for at least four hundred years, and with good reason: It has a rich, earthy flavor and velvety texture, and it’s terrifically versatile. Spread it on toast (spectacular served with a fried egg), on a sandwich, over rice or pasta, or added to a soup or sauce for a boost in flavor. It keeps well too, though it won’t last that long. And don’t let a mere 26 hours stand between you and this sauce; 24 of those hours are for mindless marinating.

11/2 pounds white mushrooms, halved

1 tablespoon salt

1 ounce dried porcini or shiitake mushrooms

1/4 cup sherry vinegar or white wine vinegar

1/2 cup roughly chopped shallot or onion

1 clove garlic, peeled

Freshly ground black pepper

1/4 cup dry sherry (optional)

Put the fresh mushrooms in a food processor and pulse until roughly chopped. Transfer to a large bowl; sprinkle with the salt and mix until the salt is distributed evenly. Cover with a cloth and let sit at room temperature for about 24 hours, stirring 3 or 4 times (the mushrooms will turn dark).

An hour before you’re ready to make the sauce, put the dried mushrooms in a medium bowl and cover with about 2 cups boiling water. Use a plate if necessary to keep them submerged and soak until soft, about an hour.

Transfer the fresh mushrooms to a food processor. Use a slotted spoon to move the dried mushrooms to the processor. Then ladle or pour in 1/2 cup of their soaking liquid, trying not to disturb the grit settled at the bottom of the bowl. Add the vinegar, shallot, garlic, and lots of pepper; pure until smooth.

Put the mushroom mixture in a pot over medium-high heat and bring to a boil, stirring occasionally. Lower the heat so it bubbles gently and cook, stirring occasionally, until the mixture appears homogenous and thick, an hour or so. (To test the consistency, dab a small spoonful onto a plate and let sit for a few minutes; if liquid is released, it needs to cook longer.)

Cool until safe to handle, then put the ketchup in a blender and pure until smooth, almost velvety in texture. Add the sherry if youвre using it and adjust the seasoning. Let cool to room temperature, then serve or store, refrigerated, in a covered container for up to 2 weeks.