Instructions

1. Grease a 3-quart, 13- x 9-inch baking dish with butter; set aside. Bring a large pot of salted water to a boil over medium-high. Add lobster tails; cook, undisturbed, until shells turn red but meat is still slightly translucent, about 2 minutes (lobster should be undercooked). Using tongs, transfer lobster to a large bowl; let cool 5 minutes. Transfer 2 cups of the cooking water to a heatproof measuring cup and set aside; reserve remaining water in pot on stovetop. Using kitchen shears, and working over the bowl to catch any juices, cut down the center of each lobster tail shell, transfer meat to a cutting board, and add shells to bowl. Remove and discard digestive tract from the lobster tails. Chop lobster meat into 1-inch pieces and place in a medium bowl; cover and refrigerate.

2. Melt 2 tablespoons of the butter in a large saucepan over medium-high. Add reserved lobster shells with any juices from bowl; cook, stirring often, until aromatic, about 2 minutes. Add onion, garlic, and thyme sprig; cook, stirring often, until onion is soft and translucent, about 3 minutes. Add wine; cook, stirring often, until almost dry, about 6 minutes. Stir in reserved 2 cups cooking water in measuring glass, and bring to a simmer over medium. Simmer, stirring occasionally, until reduced by half, about 15 minutes. Stir in milk, cream, and tarragon sprigs; cook over medium-low, stirring occasionally, 10 minutes. Remove from heat. Pour through a fine mesh strainer into a large heatproof bowl; discard solids. There should be about 4 cups lobster stock; set aside. Wipe saucepan clean; set aside. Preheat oven to 400°F.

3. While lobster stock reduces, return remaining lobster cooking water in large pot to a boil over high. Add pasta and cook for 1 minute less than package instructions for slightly less than al dente. Drain and set aside.

4. Melt 4 tablespoons of the butter in cleaned saucepan over medium until foamy. Whisk in flour; cook, whisking constantly, until bubbly and light golden brown, about 2 minutes. Gradually whisk in reserved 4 cups strained milk mixture. Cook, whisking often, until thickened, 6 to 8 minutes. Remove from heat; gradually whisk in fontina and Gruyère, whisking until melted. Add mascarpone and whisk until smooth. Stir in soy sauce, pepper, mustard, and nutmeg. Gently stir in cooked pasta and lobster meat. Spoon mixture into prepared baking dish; set aside.

5. Microwave remaining 2 tablespoons butter in a medium-size microwavable bowl on HIGH until melted, about 30 seconds. Stir in panko, Parmesan, lemon zest, and paprika. Sprinkle evenly over mac and cheese mixture in baking dish. Bake in preheated oven until bubbly and light golden on top, about 20 minutes. Remove from oven; let stand 10 minutes. Garnish with thyme leaves and tarragon leaves. Serve.