Prepare the crepes first and set aside.
Melt the butter in a frying pan on medium heat. Add the leeks and cook until they start to soften - about 3 minutes. Add in the salmon filets, flaking the fish into small pieces as it cooks.
When the fish is cooked through, sprinkle on the flour and stir to mix completely with the fish and leeks. Pour in the wine milk and cook, stirring occasionally until the mixture boils and thickens - about 5 minutes. Remove from heat and stir in 1/4 cup of cheese. Let cool about 5 minutes. Stir in nutmeg and salt and pepper to taste.
For each crepe, mound a generous 1/4 of the salmon mixture in a log shape in the center of the crepe. Fold over about 1/2 inch of the side edgges to hold in the filling, than roll the crepe up. Place the crepes seam side down in a greased baking dish. Sprinkle with remaining 1/4 cup of cheese.
Bake at 350°F for 20 minutes. Serve immediately.
Makes 12 crepes, or six servings.