In a large bowl add sugar, grate the lemon zest. With your fingers, rub the sugar and the zest together until moist and aromatic. Add the eggs, whisking after each one. Squeeze the lemon juice (about three tablespoons). Add lemon juice and half and half. Add starter and mix together.
Gradually add the dry ingredients, whisking to incorporate into batter.
Add in vanilla and melted butter. Batter will be thick. Pour into prepared loaf pan.
Bake for 70-75 minutes or until toothpick inserted in center comes out clean. Transfer to a cooling rack and let it cool for five minutes.
When cool, loosen cake from the sides of the pan and turn onto cooling rack.
Prepare the marmalade glaze. Brush glaze over warm cake and allow glaze to set for two hours.
Adapted from NY Times Cooking.If you don't have access to ground cardamom, you can replace with ground cinnamon.