Wash fresh asparagus; cut off and discard woody base of stalks.
Cook asparagus in small amount boiling water with 1/2 teaspoon salt.
Cook, covered, till tender, 10 to 15 minutes.
Meanwhile, in small saucepan combine the cream, butter, dried mint, and 1/4 teaspoon salt.
Heat and stir till butter melts and mixture is hot.
Stir a moderate amount of the hot mixture into the egg yolk.
Return to saucepan; cook and stir till thickened, 1 1/2 to 2 minutes more.
Remove from heat, stir in lemon juice.