You can make this sauce with thawed frozen peas instead of fresh, in which case they don’t need to be blanched. The sauce can be made up to 1 day ahead and refrigerated in an airtight container. Reheat over medium-low heat, adding water to thin, if necessary.

　　

Ingredients

Makes 3/4 cup

　　Coarse salt

　　1 1/3 cups shelled fresh peas

　　1 cup loosely packed watercress (1 ounce)

　　4 teaspoons cold unsalted butter

　　

Step 1

Prepare an ice-water bath; set aside. Bring a medium pot of water to a boil; add salt. Blanch the peas and watercress until bright green, about 45 seconds. Immediately transfer with a slotted spoon to the ice-water bath to stop the cooking.

　　

Step 2

Drain the peas and watercress, then puree in a blender until smooth, adding 4 to 5 tablespoons water to thin (mixture should be just thick enough to coat the back of a spoon). Pass the puree through a fine sieve into a small saucepan. Place over low heat, and whisk in the butter, 1 teaspoon at a time; whisk until emulsified. Season the sauce with salt.

　　Reprinted with permission from The Martha Stewart Living Cookbook: The New Classics by Martha Stewart Living Magazine, copyright © 2007. Published by Clarkson Potter, a division of The Crown Publishing Group.Buy the full book from Amazon.