Gradually stir powdered sugar into glaze mixture. Place saucepan of glaze in bowl of cold water. Beat with spoon until smooth and thin enough to drizzle. If glaze becomes too stiff, stir in additional milk, 1/2 teaspoon at a time, or heat over low heat, stirring constantly. Drizzle glaze over loaves. Wrap tightly and store at room temperature up to 4 days, or refrigerate up to 10 days.