Put the egg yolk in a small bowl. Add a few drops of lukewarm water and whisk well. Begin adding the olive oil in a very thin stream, whisking constantly. When the sauce thickens and forms a creamy emulsion, you can add the oil a little faster. Whisk in the shallot, parsley, tarragon, and lemon juice. Season with 1/2 teaspoon salt or more to taste. If needed, whisk in a few drops of water to loosen the mayonnaise until it's spoonable, not stiff.

Bring a large pot of salted water to a boil over high heat. Add the asparagus and blanch for 1 minute for small spears, or 1-1/2 minutes for medium spears. Transfer the asparagus with tongs to a bowl of ice water. When cool, lift the spears out of the ice water and thoroughly pat dry.

Prepare a hot charcoal fire or gas grill. Put the spears on a rimmed baking sheet or platter. Drizzle with 1 tablespoon olive oil, season with a generous pinch of salt, and toss with your hands to coat the spears evenly.

Position the grill grate as close to the coals or heat source as possible. Heat the grate and then arrange the asparagus on the grate directly over the heat with all the tips pointing in the same direction. Be sure to arrange the asparagus perpendicular to the bars so the spears don't fall through. Grill, turning the spears once with tongs, until they're blistered and lightly charred in spots, about 3 minutes total. Transfer to a platter and serve immediately, passing the mayonnaise separately.

* Note: The egg yolk in this recipe is raw, so if you're cooking for small children, the elderly, or anyone with a compromised immune system, use a pasteurized egg product instead.