Preheat the oven to 350 F.
In a stand mixer fitted with the whisk attachment, beat the egg whites until stiff peaks form; reserve.
Combine the egg yolks, milk, sugar, flour, juice, zest and salt. Beat until smooth, about 3 minutes. Fold in egg whites. Pour the mixture into an ungreased 12- x 8-inch baking dish. Place the dish in a roasting pan. Pour 1 inch of very hot water into the roasting pan, creating a hot water bath for the baking dish. Bake for 45 minutes, until bubbling at the edges and browned on top. Remove the baking dish from the roasting pan.
Serve warm or cool. Top with whipped cream.