Trim off the tough ends of asparagus spears; remove the scales with a knife. Place in a pot & cook, covered, in boiling water for 6-8 minutes or until tender-crisp; drain. Arrange the spears on a serving dish & keep warm. In the top of a double boiler combine sour cream, parm cheese, & mayo. Heat over boiling water, stirring frequently. Pour over the warm asparagus.