Preheat oven to 350°F. Grease and flour (or spray with "baking" spray) an 8x4-inch loaf pan.
Put the sugar and the orange zest in a large bowl, and rub them together with your fingers until the sugar is perfumed -- about 30 seconds. In the same bowl, whisk in the yogurt, eggs, vanilla extract, orange marmalade, and oil. Add the self-rising flour, and whisk only until the flour disappears into the batter.
Pour the batter into the prepared loaf pan. Bake until the cake puffs and browns lightly, and a skewer inserted into the cake comes out clean or mostly clean -- 45-50 minutes. Cool completely on a wire rack.
To make the glaze, whisk together the confectioners' sugar and just enough orange juice (or Cointreau or Grand Marnier) to make a smooth, pourable mixture. Pour the glaze on top of the cake. Garnish, if desired, with dried organic rose petals.