1 c. unsalted butter softened
2 c. sugar
10 large eggs separated
2 tbsp. lemon juice
2 tbsp. lemon peel grated
1 tsp. vanilla extract
1/2 c. poppy seeds
4 1/2 c. cake flour sifted
4 tsp. baking powder
3/4 tsp. salt

Preheat oven to 325°F. Butter well two 9 by 5 by 3 inch loaf pans and dust with flour, shaking out the excess. In a bowl with an electric mixer, cream the butter, then add 1 1/2 c. sugar a little at a time, and beat until light and fluffy. Beat in one egg yolk at a time, then add remaining ingredients one at a time, mixing well. Fold in egg whites gently but thoroughly into the batter. Divide the batter between the loaf pans and bake for 1 to 1 1/4 hours, or until cake tester inserted in the center of each loaf comes out clean. Let cool in the pan for 5 minutes and invert onto rack to cool completely.