Combine the butter, orange rind and juice in a saucepan. Bring to a boil. Reduce the heat and simmer until the mixture is reduced by half and slightly thickened, stirring occasionally. Set the sauce aside and keep it warm.
Snap off the tough ends of the asparagus. Cook the asparagus, covered, in a small amount of boiling water for 6-8 minutes or until tender but still a touch crisp. Drain it well.
Arrange the asparagus on a serving plate. Pour the orange sauce over the asparagus. Garnish with orange slices if desired.