Cake: Preheat the oven to 180 degrees C. Grease a 18cm round cake tin and lightly dust with flour.
In a large bowl, beat the butter and sugar with a handheld mixer until creamy. Add the eggs, one at the time until well combined. Then stir in the vanilla extract, juice and zest of tangerines. Sift in the flour mixed with baking powder and stir just enough to form a smooth cake mixture. Pour into the prepared cake tin.
Bake in the preheated oven for 25 to 30 minutes or until a skewer inserted in the middle comes out clean and dry. Remove from oven and allow to cool completely in the tin.
To Decorate: In a saucepan on low heat place the juice of 2 tangerines and 100g of caster sugar. Dissolve the sugar without stirring.
Slice 4 tangerines in 5 to 6mm thick slices. When the juice starts boiling, add the tangerine slices to the pan and simmer until it forms a syrup. The tangerine slices will turn glossy. Remove from heat and cool.
Make a water glaze mixing the icing sugar with 1 tablespoon of water. If too thick, add some more drops of water.
Flip the cake onto a cooling rack and prick with a fork. Brush the bottom and side with tangerine syrup, then flip again onto a serving plate. Pour the glaze on the surface and let is soak into the holes. Decorate the top with the caramelised tangerine slices and serve.
To decorate this cake for Christmas, just sprinkle with silver sugar sprinkle and add some tangerine leaves.