In a kettle of boiling salted water cook the asparagus for 3 to 5 minutes, or until it is tender but not limp, and drain it well in a colander. In a small saucepan melt the butter, stir in the scallion, the zest, the peppercorns, and salt to taste, and simmer the mixture for 3 minutes. Strain the butter mixture through a fine sieve into the kettle, add the asparagus and salt and pepper to taste, and heat the asparagus over moderately high heat, tossing it gently, until it is heated through.