To save time, buy fresh lobster tails and have them steamed at the store. If using whole lobster, reserve the shells to cook the meat in, and use the body and claw shells to simmer in the milk.
3 cups water
4 large lobster tails (about 28 ounces)
2 cups fat-free milk
1 teaspoon olive oil
3 tablespoons chopped shallots (about 1 large)
2 (8-ounce) packages presliced mushrooms
3 tablespoons dry sherry
1 1/2 tablespoons all-purpose flour
1/4 teaspoon freshly ground black pepper
Dash of white pepper
1 tablespoon chopped fresh basil
2 teaspoons chopped fresh tarragon
3 tablespoons whipping cream
1/4 teaspoon kosher salt
3/4 cup (3 ounces) shredded reduced-fat, reduced-sodium Swiss cheese (such as Alpine Lace)
2/3 cup panko (Japanese breadcrumbs)
2 teaspoons unsalted butter
How to Make It
Bring 3 cups water to a boil in a stockpot. Place a vegetable steamer or rack in bottom of pan. Add lobster tails. Cover and steam for 8 minutes or until done. Cool to room temperature. Remove meat from cooked lobster tails; chop meat into bite-sized pieces (you should have about 1 3/4 cups chopped meat). Cover and chill.
Place lobster shells in a large zip-top plastic bag. Coarsely crush shells using a meat mallet or rolling pin. Combine shells and milk in a small saucepan over medium heat. Bring to a simmer; cook 5 minutes (do not boil). Remove from heat; cover and let stand 30 minutes. Strain mixture through a fine mesh sieve into a bowl; discard solids. Set aside.
Preheat oven to 450°.
Heat oil in a large nonstick skillet over medium-high heat. Add shallots; sauté 2 minutes or until soft. Add mushrooms; sauté 4 minutes or until liquid begins to evaporate. Stir in sherry, and cook 1 minute.
Combine reserved milk mixture, flour, black pepper, and white pepper in a small bowl; stir with a whisk until smooth. Add milk mixture to pan; bring to a boil. Cook 1 minute or until thickened, stirring constantly. Stir in basil and tarragon; cook for 1 minute, stirring occasionally. Add reserved lobster meat, cream, and salt, stirring to combine. Divide mixture evenly among each of 4 (1 1/2-cup) gratin dishes coated with cooking spray.
Combine cheese, panko, and melted butter in a small bowl; toss to combine. Sprinkle about 1/3 cup panko mixture over each gratin. Bake at 450° for 12 minutes or until topping is browned.