Preparation

• Hard-boil the eggs: Place the eggs in a pot and cover with cold water. Bring to a boil over medium heat, cover, remove from heat and let sit 10 minutes. Transfer to an ice water bath for 10 minutes, then them remove and refrigerate until ready to use.
• Slice the leek almost in half, stopping ¾-inch from the root. Rinse under cold water to remove any dirt or grit between the layers. Keeping the base of the leek intact, trim the end to remove the root.
• Bring 2 quarts salted water to boil. Submerge the leeks in the boiling water, lower the heat to medium, and simmer 12 minutes.
• Carefully remove the leeks and place in an ice water bath to stop the cooking. Drain them on paper towels, then slice through the leek completely, separating the halves. Place on a serving dish and set aside.
• In a small bowl, whisk together the mustard, vinegar, the olive oil and a pinch of salt and pepper until combined. Stir in the tarragon. Pour the vinaigrette over the leeks and turn to coat. Cover and refrigerate at least 3 hours and up to 2 days.
• Bring the leeks to room temperature 2 hours before serving. Peel the hard-boiled eggs and separate the white and the yolk. Coarsely chop the egg. Garnish the leeks with chopped egg and chopped tarragon and serve.