Preheat the oven. Line the bottom of the pan with baking paper and grease the sides with butter. Beat sugar with butter until pale and whipped. Gradually add the eggs along with dry ingredinces. Beat in orange zest and spoon the mixture into the pan. Spread mixture equally and bake in the oven for 30 minutes. Meanwhile warm up orange juice with icing sugar until dissolved. Take out the cake when finished and using pastry brush spread all of the syrup evenly on top of the cake. Let it cool down before cutting into portions. Can be served with dollop of creme fraiche.