Step 1

Place potatoes in large saucepan and add water to just cover. Add salt and bring to boil over high heat. Reduce heat to maintain simmer and cook until tip of paring knife inserted into potato meets no resistance, 8 to 10 minutes. Drain potatoes and return to saucepan over low heat. NOTE: I steamed my potatoes in my Instant Pot Pressure Cooker for 5 minutes, drained and returned back to the pot with the WARM cycle turned on.Cook, shaking saucepan occasionally, until any surface moisture on potatoes has evaporated, about 1 minute. Off heat, mash potatoes well. Stir in butter until melted. Whisk cream and egg yolk together in bowl; stir into potatoes. Season with salt and pepper to taste. Cover to keep warm and set aside. NOTE: I added a little more cream, until the potatoes were spreadable consistency.

Step 3

Set 8-inch square broiler-safe baking dish on rimmed baking sheet. NOTE: I opted to make this recipe in a 12" skillet, rather than using a baking dish.Sprinkle shrimp with ¼ teaspoon salt and baking soda in bowl and toss to combine. Refrigerate until needed.

Step 4

Melt 3 tablespoons butter in medium saucepan over medium-low heat. Add leek and thyme and cook, stirring occasionally, until leek is softened, 6 to 7 minutes. Add wine and cook, stirring occasionally, until wine has evaporated, about 5 minutes. Add flour and cook, stirring constantly, for 1 minute. Add clam juice (or Lobster base) and stir until mixture is smooth. Stir in cream, pepper, and remaining ½ teaspoon salt. NOTE: I would wait to add the salt, once you've added the smoked salmon, as it adds salt in itself. Increase heat to medium-high and bring to simmer. Lower heat to maintain simmer and cook, stirring frequently, until mixture resembles thick chowder, 10 to 13 minutes.

Step 5

Stir cod, salmon, and shrimp into sauce and return to simmer. Cover and cook, stirring every 2 minutes and adjusting heat if needed to maintain simmer, until shrimp are opaque and just cooked through, 4 to 6 minutes. Off heat, stir in parsley. Transfer filling to prepared dish. Likewise, leave the filling in an oven-proof skillet.

Step 6

Adjust oven rack 8 inches from broiler element and heat broiler. Spoon topping over filling, starting at edges and working toward center. Smooth with rubber spatula, making sure to seal around edges of dish so no seafood or sauce is exposed. Using back of spoon or tines of fork, make pattern on topping. Melt remaining 1 tablespoon butter and drizzle over topping. Broil pie, still on sheet, until topping is golden brown and crusty and filling is bubbly, 6 to 7 minutes (watch closely). Let cool for 10 minutes before serving.