CHEDDAR-WALNUT GOUGèRES

Steps:

• Set a rack in the center of the oven and heat to 400 degrees. Line 2 large baking sheets with parchment paper.
• Put the butter, milk, salt and 1/2 cup water in a medium saucepan, and bring to a boil. Add the flour all at once, set heat to medium-low and stir without stopping until the mixture pulls away from the pan easily and comes together in a ball. Keep stirring energetically for 3 minutes more; the drier the dough, the better the gougères. Scrape the dough into a mixer with a paddle attachment (or into a large bowl, if you're mixing by hand), and let sit for 1 minute.
• With the mixer at medium speed, add the 4 eggs one by one, and beat for 1 minute after each goes in, scraping the bowl as needed. As you're working, the dough may break into curds; just keep going - it's always fine once the egg white goes in.
• Beat in the egg white, then the mustard. Reduce the mixer speed to low, and blend in the cheese followed by the nuts. Give the dough a few good beats with a sturdy spatula.
• Working with a small cookie scoop or 2 spoons, scoop balls, each about 2 teaspoons, onto the sheets, leaving an inch between each. (Gougères are excellent baked from frozen. They can be frozen at this point; set them in an airtight container once frozen solid.)
• Working with one baking sheet of fresh gougères at a time, slide the gougères into the oven and turn the heat down to 375. Bake for 22 to 24 minutes, or until the gougères are puffed, golden and firm enough to pick up. (If baking frozen gougères, arrange them on a lined baking sheet, and leave at room temperature while you heat the oven. You may need to bake them a couple minutes more, so keep an eye on them.) Serve immediately. Baked gougères can also be reheated briefly in a 350-degree oven.