Grease the gugelhupf tin and preheat the oven to 160C, Gas Mark 3
Cream together the butter and sugar.
Mix in the eggs one at a time.
Zest the orange and squeeze out the juice.
Add half the orange zest to the mixture with the flour and baking powder.
Mix together and add the orange juice.
Place the mixture in the gugehupf tin and bake for 75 - 90 minutes until a skewer comes out clean.
Leave to cool for ten minutes in tin then remove.
Mix the icing sugar with the water and orange juice and drizzle over the cake.
Use the remaining orange zest to decorate.