Preheat oven 350 ° .
Chop the tuna very thin.
In a saucepan, melt butter, add flour and stir the mixture over a fire a few seconds to get a white texture. Add the milk. Stir constantly for a thick sauce (béchamel).
Stir in the tuna, egg yolks and egg whites, stiffly beaten. Salt and pepper to taste.
Finally, pour the mixture into a nonstick mold (or whatever, but buttered) and bake for 25-30 minutes.
Serve immediately with a salad.