Combine first 6 ingredients in a bowl; beat at medium speed of a mixer until smooth. Beat at high speed 15 seconds; set aside.
Divide 1 tablespoon reserved pan drippings evenly among 6 popover cups, and coat sides of cups with cooking spray. Place popover pan in a 400° oven for 3 minutes. Divide batter evenly among prepared cups, and bake at 400° for 10 minutes. Reduce oven temperature to 325°, and bake an additional 25 minutes or until golden. Serve immediately.
Note: Substitute 1 tablespoon vegetable oil and 1/4 teaspoon salt for 1 tablespoon pan drippings in Yorkshire Pudding, if desired.