Directions

1. Preheat oven to 400 degrees. Cover potatoes with water by 2 inches in a medium stockpot. Add 1 tablespoon salt, and bring to a boil. Reduce heat; simmer, partially covered, until tender, about 20 minutes. Drain. Mash potatoes or pass through a ricer. Stir in 4 tablespoons butter, the milk, 1 teaspoon salt, and 1/4 teaspoon pepper. Stir in yolks.
2. Melt 4 tablespoons butter in a large skillet over medium-high heat. Add leeks, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper. Cook, stirring occasionally, for 2 minutes. Cover; reduce heat to medium-low. Cook, stirring occasionally, until tender, about 8 minutes.
3. Stir in flour, and cook for 1 minute. Stir in stock, and bring to a boil. Reduce heat, and let simmer for 2 minutes. Stir in lobster and dill, and divide among four 10-ounce baking dishes. Top each with 3/4 cup potato mixture, leaving a 1/2-inch border, and a butter pat. Garnish with dill sprigs. Bake on a baking sheet until bubbling, about 30 minutes. Let stand for 15 minutes before serving.