1. Snap off the woody ends from the asparagus spears. Brush a ridged grill pan with the oil and heat over medium-high heat until the pan is very hot. Cook the asparagus, turning once, for about 6 minutes, until the asparagus has grill marks and is just tender (thick spears may take longer, so reduce the temperature as needed so the asparagus cooks without charring).

2. Meanwhile, make the sauce. Boil the vinegar until reduced by half. Remove from the heat, and add 2 tbsp water. One at a time, whisk in the egg yolks.

3. Return the saucepan to a very low heat and whisk until the mixture is thick and pale. Remove from the heat and gradually whisk in the melted butter. Stir in the lemon juice. Season with salt and pepper.

4. Divide the asparagus between serving plates. Spoon the sauce over the asparagus, and serve at once.