TUNA AU GRATIN
• 2¼ pounds mussels
• 5 tablespoons white wine
• 1/4 cup (1/2 stick) butter
• 2 tablespoons sunflower oil
• 3 tablespoons all-purpose flour
• 2¼ cups milk
• 1 pound 2 ounces canned tuna, drained and flaked
• 1 tablespoon chopped fresh parsley
• 2 scallions or large shallots, very finely chopped
• juice of 1 lemon
• 2 eggs, separated (optional)
• 3 tablespoons bread crumbs
If your mussels have not been pre-scrubbed, scrape their shells with the blade of a knife and remove the "beards," then scrub under cold running water. Discard any mussels with broken shells or any that do not shut immediately when sharply tapped.
Put them into a pan with the wine, 5 tablespoons water, and a pinch of salt. Cover and cook over high heat shaking the pan occasionally for 4-5 minutes, until the shells have opened. Remove the mussels with a slotted spoon and reserve the cooking liquid.
Discard any mussels that remain closed. Strain the cooking liquid through a cheesecloth-lined strainer into a bowl. Remove the mussels from their shells, cut in half with kitchen scissors if they are large, and put into the bowl of cooking liquid.
Preheat the oven to 400°F.
Heat half the butter with the oil in a pan. Stir in the flour and cook, stirring constantly, for 2 minutes. Gradually stir in the milk, a little at a time Cook stirring constantly, for about 10 minutes until thickened.
Add the tuna, parsley and scallions or shallots. Using a slotted spoon add the mussels and stir in 3/4 cup of the reserved cooking liquid. Season to taste with salt and add the lemon juice.
Whisk the egg whites, if using in a clean, dry bowl until stiff.
Beat the egg yolks, if using, in another bowl, stir in a little of the sauce to prevent them from curdling, and add to the pan. Remove the pan from the heat and fold in the egg whites.
Divide the mixture among individual gratin dishes, sprinkle with the bread crumbs and dot with the butter. Bake for 5-10 minutes, until golden brown. Serve immediately straight from the dishes.