- In a bowl, whisk together the egg yolk, mustard and vinegar. Slowly drizzle in one-third of the oil, whisking constantly. When the emulsion starts to resemble mayonnaise, drizzle in the remaining oil while whisking. Season with salt and pepper. Stir in the truffle oil, if desired. Refrigerate until ready to serve.
- Preheat the grill, setting the burners to high.
- Cut the base of each artichoke stem. With scissors, cut the pointed tips of the artichoke leaves. Place each artichoke at the centre of a piece of foil and drizzle with the oil to coat well. Season with salt and pepper. Tightly seal the foil around the artichokes.
- Place the foil packets on the grill. Close the cover and cook for 20 minutes, turning halfway through.
- Open the foil packets. Place the artichokes directly on the grill and continue cooking until slightly charred on all sides. Open the artichoke leaves up to resemble a flower. Place on a serving dish with the mayonnaise at the centre of the table for your guests to serve themselves.