- Preheat the oven to 375 ºF (190 ºC) and line muffin tins with paper cups.
- Sift the flour with 1 cup (225 g) of sugar, baking powder and salt into a large mixing bowl. Make a well in the center of the flour mixture and add the oil, buttermilk, vanilla and tangerine zest. Beat one minute with electric beaters. Add tangerine juice and egg yolks and beat another minute.
- In a separate bowl and using clean beaters, whip the egg whites until foamy. Gradually pour in the remaining ½ cup (100 g) sugar and whip until whites hold a stiff peak. Fold whites gently into batter and spoon into muffin cups. Bake for 15 minutes or until cupcakes spring back when gently pressed. Allow to cool.
- For the frosting, beat the butter until fluffy. On low speed beat in the icing sugar until smooth. Beat in the vanilla, zest and tangerine juice. If icing is too thin, add a touch more icing sugar. Spread icing onto cupcakes, garnish with sprinkles and serve.
*For a chocolate frosting, replace ½ cup (65 g) with ½ cup (60 g) of cocoa powder when adding, and then stir in 2 oz (60 g) of melted dark chocolate at the end.