Snap off the tough asparagus ends and discard. Peel ends of spears with sharp paring knife or vegetable peeler, if desired.
Place 5 cups (1250 mL) of water and 1 teaspoon (5 mL) salt in a large deep skillet and bring to a boil. Add asparagus spears. Boil uncovered for 4 to 5 minutes for thin spears, or up to 8 to 10 minutes for thick spears, or until crisp-tender. Drain well. Transfer asparagus to serving plate.
In a jar with a tight fitting lid, combine orange juice, lemon juice, sugar, mustard, salt and pepper; shake well. Add vegetable oil. Shake well again. Pour as much dressing as wanted over warm asparagus. Sprinkle with egg yolk, if desired. Serve at room temperature.
Note: The salad can also be served chilled. Do not top spears with dressing until just prior to serving.