Preheat oven to 325°F; grease an 8x8 inch baking pan.

Beat egg whites to stiff peaks; set aside.

Separately beat yolks and sugar until pale; beat in melted butter and mashed bananas.

Mix in flour; slowly pour in lukewarm milk, mixing on low.

Gently fold in stiff egg whites. Batter will be very thin and lumpy.

Pour into pan; bake 50 to 60 minutes, until top is golden and center jiggles slightly. Cool completely before slicing.