If using live lobster, steam or boil 1.5–2 lb lobster for 8–10 minutes until shells are bright red; cool briefly and remove meat, discarding shells. Coarsely chop lobster meat to bite size (about 1.25 lb after trimming). If using pre-cooked lobster, chop to bite size. Pat lobster and shrimp dry with paper towels. Cut shrimp into 1/2" pieces if large; leave tails on if desired. Gently fold lobster, shrimp and crab meat together and refrigerate briefly while you prepare the base.

Cobblestone Base (Bread & Veg)

Preheat oven to 400°F (200°C). Spread bread cubes on a baking sheet and toast in the oven 6–8 minutes until slightly crisp but not browned. Remove and set aside.

In a large skillet over medium heat, melt 3 tbs butter. Add minced shallots and sauté 2–3 minutes until softened. Add garlic, diced celery and red pepper; cook 3–4 minutes until vegetables are tender-crisp. Stir in corn kernels and cook 1 minute more.

Creamy Lobster Sauce

Sprinkle 2 tsp flour over the vegetables in the skillet and stir to coat; cook 1 minute to remove raw flour taste.

Deglaze the pan with 1/2 cup dry white wine, scraping up any browned bits; simmer 2 minutes to reduce slightly. Add 1/2 cup fish or chicken stock and bring to a gentle simmer for 2 minutes.

Reduce heat to low and stir in 3 tbs heavy cream and 1/2 cup whole milk. Add 1 tsp Dijon mustard, 1 tbs fresh lemon juice, 1 tsp Old Bay seasoning, 3/4 tsp salt and 1/2 tsp black pepper. Simmer gently 2–3 minutes until the sauce begins to thicken slightly.

Stir in 1 cup grated Gruyère (reserve 1/4 cup for topping) and 2 tbs chopped tarragon until cheese melts and sauce is smooth. Taste and adjust seasoning.

Combine & Bake

Remove the skillet from heat and let the sauce cool 1–2 minutes. Whisk the lightly beaten egg yolk into a small bowl. Temper the yolk by stirring 2 tbs of the warm sauce into the yolk, then stir the yolk mixture back into the skillet to help bind the filling.

Fold the chopped lobster, shrimp and crab gently into the sauce mixture until evenly coated. Add the toasted bread cubes and fold to combine so bread absorbs some sauce but does not become mushy.

Transfer the mixture to a lightly buttered 9" x 9" (or similar) baking dish, pressing lightly to create an even surface.

Finish & Garnish

In a small bowl, combine 3/4 cup panko breadcrumbs, 1 tsp olive oil and 1/4 cup reserved grated cheese; toss with 1/2 tsp lemon zest. Sprinkle this crumb mixture evenly over the top of the cobblestone.

Bake in preheated 400°F (200°C) oven for 12–15 minutes until the topping is golden brown and the filling is bubbling at the edges. If you want a deeper brown top, broil 1–2 minutes watching carefully.

Remove from oven and let rest 5 minutes. Sprinkle chopped chives and remaining lemon zest over the top. Serve warm with lemon wedges on the side.