Sorrel can be tricky to find in markets, although I do see it in farmer's markets occasionally. Your best bet is to grow it. Sorrel is indestructible in the garden and grows really easily. I planted a few plants in 2004 and they're still going strong, and expand every year. You can buy sorrel seeds online or in most seed catalogs. Or you can use wild sorrel.
Keyword: sauce, sorrel
Author: Hank Shaw
1/4poundsorrel leaves,stems removed
2tablespoonsvermouth,or chicken or vegetable stock
Salt and white pepper to taste
Chiffonade the sorrel by curling up a few leaves at a time and slicing them very thin.
Pour the cream in a small pot and bring it to a simmer. Doing this will prevent it from curdling when it hits all that acidic sorrel in a few minutes.
Meanwhile, in another small to medium pot, heat the butter over medium heat and add the sorrel. Cook the sorrel, stirring often, until it melts -- it will cook down a lot and turn Army green. When it does, stir in the cream and bring the sauce to a bare simmer. It will be pretty thick, so you'll want to add the vermouth or stock to thin it out. You can add another tablespoon if you want the sauce even thinner. Add salt and white pepper to taste and serve.
Once you make this sauce, you'll need to use it; it doesn't keep well, although it will be OK on the stovetop kept warm for an hour or two.