1) Preheat the oven to 400°F. Lightly grease and flour the wells of a muffin pan; or line the pan with paper liners, and grease the liners.
2) To make the cupcakes: Whisk together all the dry ingredients, then stir in the chopped clementines or tangerines.
3) In a separate bowl, whisk together the vanilla or Fiori, vegetable oil, and orange juice.
4) Stir the wet ingredients into the dry ingredients; don't over-mix, stir just until everything is moistened.
5) Spoon the batter into the prepared muffin cups, filling each nearly full. A level (to slightly heaped) muffin scoop of batter for each cupcake works well here.
6) Sprinkle the tops with coarse white sparkling sugar, if desired. If you plan on icing the cakes, skip the sparkling sugar.
7) Bake the cupcakes for 15 to 18 minutes, until they've domed nicely. They won't brown; that's OK. to test for doneness, stick a toothpick into the center of one of the cupcakes in the middle of the pan; if it comes out free of moist crumbs, the cupcakes are done.
8) Remove the cupcakes from the oven, and after 5 minutes transfer them to a rack to cool.
9) To make the frosting: Whisk all of the ingredients together, adding 3 tablespoons orange juice to start. Dribble in more, a bit at a time, until the frosting is as soft as you like it. Drizzle and spread the frosting over the cooled cupcakes.
Yield: 12 cupcakes.