Popovers often require a special pan. All you need for these is a muffin tin!
Arrange a rack in the bottom third of the oven; preheat to 425°. In a blender, puree the milk, eggs, and butter. Add the flour, 1/2 cup cheese, the thyme, nutmeg, salt, and pepper; puree.
Generously spray 12 standard-size muffin cups with cooking spray. Divide the batter among the cups, about 1/4 cup in each. Sprinkle the remaining 1/4 cup cheese on top. Bake until puffed and deep brown, 25 to 35 minutes. (Do not open the oven door.) Carefully remove the popovers from the cups. Pierce the sides of each popover with a sharp knife to release some of the steam. Serve immediately.