Preheat the oven to 180ºC (160ºC fan).
Grease and line an 8 inch cake tin with greaseproof paper.
Thinly slice the oranges and lay them in the bottle of the cake tin so they don't overlap.
Cream the sugar and butter together in a bowl with a wooden spoon.
Mix in each egg one at a time.
Sift in the flour and mix until smooth.
Add the zest and juice of 1 orange to the mixture and mix well.
Spoon the batter into the cake tin being careful not to move the oranges.
Bake for 30-45 minutes. The cake should be golden on the outside and the skewer should come out clean. Remove from the oven and allow to cool while you make the drizzle. It might take up to an hour depending on your oven just keep an eye on it.
In a small pan, mix the juice of 1 orange with the icing sugar and 2 tablespoons of water.
Warm on a medium heat and keep stirring as the liquid turns into a syrup.
Using a knife loosen the cake from the edges of the tin. Place a plate on the cake tin and turn it over to release the cake and show the orange slices on top. Poke holes all over the sponge with a skewer just over half way down.
Take the syrup off the heat (careful, it's hot!) and pour all over the cooling sponge.
Leave for a few minutes for the drizzle to sink in. Best served when it is still warm.