In a medium mixing bowl, whisk together 1 cup of all-purpose flour, 2 large eggs, 2 cups of whole milk, and 2 tablespoons of melted unsalted butter until the mixture is smooth. Allow the crêpe batter to rest for at least 20 minutes at room temperature.

Heat a non-stick skillet over medium heat and lightly grease it. Pour about ¼ cup of batter into the skillet and swirl to coat the pan evenly. Cook for 1-2 minutes until edges lift slightly, then flip and cook for another 30 seconds. Stack cooked crêpes on a plate.

In a large skillet, melt 2 tablespoons of unsalted butter over medium heat. Add 1 finely chopped shallot and 2 minced garlic cloves, sauté for about 2-3 minutes until fragrant. Mix in 1 cup of cooked shrimp, 1 cup of cooked crab meat, and ½ cup of dry white wine, cooking until the liquid is reduced. Stir in ½ cup of heavy cream, 2 tablespoons of fresh parsley, and lemon zest. Season with salt and pepper to taste, then remove from heat.

In a saucepan, melt 3 tablespoons of unsalted butter over medium heat, gradually whisk in 3 tablespoons of all-purpose flour to form a roux, cooking for about 2 minutes. Gradually whisk in 2 cups of warmed milk, mixing continuously until thickened, about 5-7 minutes. Season with a pinch of nutmeg, salt, and pepper.

Lay a crêpe flat, spoon a portion of the seafood filling along one edge, roll it up, and place seam-side down in a greased baking dish. Repeat with remaining crêpes, arrange side by side. Pour béchamel sauce over crêpes and sprinkle with 1 cup of grated Gruyère cheese.

Preheat oven to 375°F (190°C). Bake assembled crêpes for about 20 minutes, or until the top is bubbly and golden brown. Garnish with chopped chives or parsley before serving hot.