Drain asparagus, reserving liquid. Finely chop asparagus. Combine asparagus and liquid to yield 1 cup, discarding any fibrous pieces. Set mixture aside.
Melt butter in top of a double boiler over boiling water; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually stir in milk; add asparagus mixture and salt.
Cook over boiling water, stirring constantly, until mixture coats a metal spoon. Remove from heat.
Beat egg yolks. Add one-fourth of hot asparagus sauce to yolks, stirring well; return to hot mixture. Cook over boiling water, stirring constantly, until thickened and bubbly. Remove from heat and cool.
Beat egg whites (at room temperature) until stiff but not dry. Fold into asparagus mixture. Spoon into a greased 1 1/2-quart souffle dish. Bake at 325° for 1 hour or until golden brown.