Cream shortening or butter in the large bowl of an electric mixer. Gradually add the sugar and beat until fluffy. Separate the eggs into two bowls. Briefly whisk the yolks together. Stir seeds or poppy filling into the whisked egg yolks, add to the mixer bowl. Stir the baking soda into the sour cream or the non-dairy creamer mixture, add to mixer. Add the flour and vanilla and mix only until the flour is fully incorporated into the batter. In a separate mixing bowl, beat the egg whites until they hold soft peaks. Fold the egg whites into the batter.
Gently put the batter into the prepared pan(s), and quickly rotate the pan(s) against the counter to remove any large bubbles. Bake for 1 hour or until a toothpick inserted in the middle comes clean.
This cake may be glazed with a mixture of melted butter (1 T.), confectioner's sugar (1 cup) pure vanilla extract (1 tsp.), and water (enough to reach a thin spreading consistency). Place under the broiler until the glaze just melts.