Stir the liquid ingredients into the dry ingredients, stirring the batter until just mixed. (Do not over beat.)
Preheat a popover pan just until hot. Brush the cups with melted butter and fill them half full of batter.
Bake for 20 minutes at 450°F. Turn the heat down to 375°F and bake for an additional 10 minutes, turn off oven and do not open oven and leave in oven for an additional 10 minutes.