Moist orange cake

This works by starting with a simple cake, already moist because of the almonds instead of flour, and then makes it moister by adding moisture (in the form of a fruit syrup) after cooking. The one drawback is that you have to make it the day before you want it.

Cake Ingredients
1.5 oz breadcrumbs (a bit stale is good, or dry the bread slightly)
3.5 oz ground almonds
7 oz caster sugar
1.5 tsp baking powder
4 eggs
7 fl oz sunflower oil (or, if you're rich, 1 fl oz almond oil and 6 fl oz sunflower oil)
Zest of 1 large orange
Zest of 0.5 standard/large lemon
Syrup Ingredients
juice of 1 large orange
juice of 0.5 standard/large lemon
3 oz caster sugar
2 cloves
1 cinnamon stick
(optionally, 1-2 stars of star anise, if you like the taste, and a dash of orange flower water)
First, invoke the goddess Rotunda, because she'll surely be visiting you soon.
Mix the dry ingredients, beat in the oil and eggs, and then add the zest. Put the batter in a pre-oiled <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />8 inch cake tin. Put into a cold oven (not preheated) and turn the heat to 375 degrees, baking for about 45 minutes. Use a cake skewer to test that it's done - if it's not , it soon will be. Leave it in the tin to cool for a few minutes, then turn it onto a high-rimmed plate (you'll see why when you do this!).
About 10 minutes before you take the cake out of the oven, mix the fruit syrup ingredients in a large saucepan (except the orange flower water), and melt them together over a medium heat. Once the sugar has dissolved, bring to the boil and simmer gently for 5 minutes, then allow to cool a little, while you test the cake and put it on the plate.
If you're adding orange flower water to the syrup, do it now.
Use a skewer to make holes in the cake, and, while cake and syrup are still warm, pour the syrup over and into the cake, aiming for the holes so the syrup permeates the cake. (Leave the cinnamon stick etc in the pan, of course.) As the cake cools it will start to leak a bit: baste it, so as much of the syrup is soaked up as possible. This can take ages, and you might be left with some syrup that just doesn't get soaked up. Eat that, or add it to fruit salad.
Finally, put foil over the top of the cake, and leave it in the fridge overnight, to let the flavours settle. It keeps well, too (provided you put it at the very back of the fridge behind an uninteresting salad and don't let your boy/girlfriend see it). Serve still slightly cold, sprinkled with a little icing sugar. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Is castor sugar the same as granulated sugar?

a quick Google for caster sugar provided: "Also called superfine sugar. It is pulverized granulated sugar. It can be purchased or prepared at home by whizzing some granulated sugar in the blender."

Could you please translate what "ZEST of 1 large orange" means?

 The zest is the outermost part of the peel of a citrus fruit. You get it off with either a  zester, a grater or vegetable peeler, in which case you would then mince it finely for a cake. Try to use an organic orange to avoid nasty chemicals.

Could you convert the recipe to U.S. measurements?

Here is a good Internet source for that http://www.recipes4us.co.uk/us_cups_to_weight.htm

Is the cake tin round or square? how deep should it be?

The recipe simply says to put the batter in a pre-oiled  8-inch cake tin. It does not mention a specific form of a tin so my guess is this to be a matter of taste.