Line the base of the cake tin and grease the sides.
Preheat the oven to 180°c (Gas Mark 4, 350°f)
Beat the margarine and sugar together, either in a free-standing mixer or by hand, until light and fluffy.
Mix the ground almonds, polenta and baking powder in a separate bowl.
Add some of the almond mixture and beat into the margarine/sugar mixture, followed by beating in 1 egg. Continue alternating until the eggs and almond mixture are all mixed in.
Finally, beat in the orange zest.
Put the mixture into the greased cake tin and level and best as possible.
Bake in the middle of the oven for 40 minutes. The cake may still seem a little wobbly, but a cocktail stick should come out clean.
Leave the cake in the tin, while you make the syrup.
Mix the orange juice and icing sugar in a small pan. Bring to a boil (the sugar should be completely dissolved.
Use a cocktail stick to make several small holes all over the cake. Spoon over the orange syrup Spread the syrup around, so it sinks into the cake.
Leave the cake to completely cool in the tin. Then take out and serve.