Whisk together flour, salt, and sugar. Separately, whisk together butter, egg, and milk. Pour liquid mixture into the flour and mix until just combined.
Grease popover cups. Pour batter into greased cups, filling them ½ to ⅔ full.
Bake at 450F for 15 minutes, then reduce oven temperature to 350F and bake for another 20 minutes, until crusty and brown. Remove popovers from oven and turn out immediately onto a cooling rack. Slit the sides with a sharp knife to let steam escape. Serve immediately.
This recipe was adapted from Martha Stewart.