Blend butter, egg yolks, milk and sugar. Mix flour, baking powder, salt and cardamom. Stir in egg yolk mixture. Beat egg whites until fluffy but not dry. Fold into flour mixture. Heat æbleskiver/monk's pan until water droplets sizzle (medium-low heat). Spoon ½ teaspoon butter into each cup. Spoon 1 rounded tablespoon batter into each cup. Cook about 2 minutes each side using a knitting needle/lond wooden skewer to turn balls. If heat is too high, centers will be doughy. Dust each with powdered sugar. Serve hot.
Notes: A variation is to spoon 1 teaspoon applesauce onto center of uncooked batter. Top with ½ teaspoon batter.