Heat the oven to 350F/Gas 4/180C. Butter a 9-inch cake pan and line the bottom with parchment paper. Butter the paper and set aside.

In a medium bowl, mix the flour, baking powder, and salt.  Set aside.  Cream the butter and sugar well for several minutes, until it is very pale and thick.

Add the eggs one by one, beating well after each addition, then add the zest. Add the flour mixture all at once, and beat well, then slowly add the clementine juice until it is incorporated.

Pour the batter into the prepared cake tin, and bake for 35-40 minutes - or until an inserted skewer comes out clean (If it starts to brown too much on the top, cover loosely with a sheet of foil.)

Allow cake to cool in pan for 15-20 minutes on a wire rack. Then invert onto a plate, remove the parchment paper and allow to cool completely before glazing.

To make the icing, stir the clementine juice into the icing sugar until you have the right spreading consistency. Using a skewer, dowel, or toothpick, poke holes through entire cake to allow glaze to seep down into it. Pour the icing onto the cake and spread with a spatula or butter knife, allowing the icing to drip down the sides of the cake.