01 - Whisk together flour and salt in a mixing bowl. Add eggs, then gradually whisk in milk until completely smooth. Stir in melted butter until incorporated. Let batter rest at room temperature for 20 minutes to allow flour to hydrate.
02 - Melt butter in a small saucepan over medium heat. Whisk in flour and cook for 1 minute until foamy but not browned. Gradually whisk in warm milk, bringing to a gentle simmer while stirring constantly. Cook until thickened, about 3-4 minutes. Season with nutmeg, salt, and white pepper. Remove from heat and keep warm.
03 - Heat an 8-inch nonstick skillet over medium heat. Lightly brush with butter. Pour approximately 1/4 cup batter into skillet, swirling quickly to coat bottom evenly. Cook until edges begin to lift and bottom is golden, 1-2 minutes. Flip and cook for 30 seconds longer. Repeat to make 8 crêpes, stacking between parchment paper to prevent sticking.
04 - Melt butter in a skillet over medium heat. Add shallot and garlic, sautéing until translucent, about 2 minutes. Pour in white wine and simmer until almost completely evaporated. Add shrimp, crab meat, and heavy cream, cooking just until heated through. Remove from heat and stir in parsley, lemon zest, salt, and pepper.
05 - Preheat oven to 375°F. Butter a baking dish lightly. Place a crêpe on clean work surface and spoon seafood filling down the center. Roll up tightly and place seam-side down in prepared baking dish. Repeat with remaining crêpes and filling, arranging snugly.
06 - Pour prepared béchamel sauce evenly over the filled crêpes. Sprinkle Gruyère cheese across the top. Bake for 12-15 minutes until sauce is bubbling and cheese is lightly golden.
07 - Remove from oven and let rest for 2-3 minutes. Garnish with chopped fresh chives or parsley if desired. Serve immediately while hot.