Place egg whites in a large bowl; let stand at room temperature for 30 minutes. Generously grease (with shortening) and flour a 10-in. tube pan.
In a large bowl, cream butter and sugar until light and fluffy. Add egg yolks, one at a time, beating well after each addition. Beat in lemon peel and extracts. In another bowl, mix the flour, baking powder, salt and cardamom; add to the creamed mixture alternately with milk, beating well after each addition.
With clean beaters, beat egg whites on medium speed until soft peaks form. Fold into batter.
Transfer to prepared pan.
Bake at 350° for 60-70 minutes or until a toothpick inserted in center comes out clean.
Cool in pan for 10 minutes before removing to a wire rack to cool.
Sprinkle with powdered sugar.
Store in an airtight container at room temperature.