Preheat the oven to 325 degrees. In a large bowl, bring the egg whites to room temperature. In a small bowl, combine 1 tablespoon water, the lemon juice and vanilla; set aside. Sift into another bowl 1/2 cup sugar, the flour and salt.
With an electric mixer, whip the egg whites for 1 minute. Add the water mixture and cream of tartar. Whip at high speed until the egg whites are fluffy. Gradually beat in the remaining sugar, beating until the mixture holds a stiff, mounded peak. (Do not overbeat; the mixture should not look dry.).
Sift half the flour mixture over the whites and fold in with a wide rubber spatula. Repeat with the remaining flour mixture.
Spoon the batter into a 10-inch tube pan with a detachable bottom and smooth the top. Bake until the top is golden and springs back, 40 to 45 minutes.
Cool the cake upside down for about an hour, centering it over a large bottle. Run a knife around the cake edges, inner and outer, and, holding the tube, remove the cake. Run a knife between the cake and the bottom of the pan and invert the cake onto a cutting board. Using a large serrated knife, cut the cake horizontally into thirds.
Using an electric mixer, whip the cream at high speed until thickened. Gradually whip in sugar. When soft mounds begin to form, beat in the Curaçao until the icing is firm.
Assemble the cake on a serving dish, spreading the icing between the layers, then over the sides and top. Chill until ready to serve. YIELD. 10 servings.