In another large bowl, whip the egg whites until foamy. Add the cream of tartar and beat until soft peaks form when the beater is raised. Gradually add the remaining tablespoon of sugar and beat until stiff peaks form. With a spatula, gently fold 1/3 of the egg whites into the egg yolk mixture to lighten. Add and fold in the remaining egg whites until there are no remaining streaks of flour, and the eggs are well incorporated. Gently spoon the batter into the prepared pan, filling the cavities about 1/2 full. Do not smooth tops.