Cranberry Muffins With Walnut Crumb Topping

Name: Cranberry Muffins With Walnut Crumb Topping
Ingredients: 1/4 cup walnut pieces; 1/2 cup all-purpose flour; 2 tablespoons granulated sugar; 2 tablespoons light brown sugar; 1/4 teaspoon baking powder; Pinch of salt; 2 1/2 tablespoons unsalted butter, melted; 2 cups all-purpose flour; 1/2 cup plus 1 1/2 tablespoons granulated sugar; 2 teaspoons baking powder; 1/2 teaspoon baking soda; 1 cup plain low-fat yogurt; 1 large egg, lightly beaten; 1 stick (4 ounces) unsalted butter, melted and cooled; 1 1/2 cups fresh or frozen cranberries; 1 cup confectioners' sugar; 1 1/2 tablespoons water