Beat the eggs and sugar together for 5 to 10 minutes with an electric mixer. With a rubber spatula, alternately fold in half the flour, cardamom (or ginger), and sour cream, and then the remaining flour. Lightly stir in the melted butter and set the batter aside for 10 minutes. Heat waffle iron until it is so hot that a drop of water sputters when flicked across its surface. Pour about 3/4 cup of the batter in the center of the hot iron. Close the top and cook over direct heat for 5 minutes. Serve with lingonberry or another tart jam.