Almond, Ricotta and Polenta Cake

From The River Cafe Classic Italian Cookbook by Rose Gray and Ruth Rogers
For 10-12; makes 1 x 26 cm round cake

225g unsalted butter, softened, plus a little for the tin
250g blanched almonds (I successfully substituted almond meal)
100g fine polenta (maize flour)
finely grated zest of 6 lemons
250g caster sugar
6 large free-range organic eggs, separated
300g fresh ricotta cheese
juice of 3 lemons
icing sugar, for dusting

PREHEAT the oven to 150 C.  Butter a 26cm round cake tin and line it with greaseproof paper.
COARSELY chop the almonds in a food processor.  Combine with the polenta flour and lemon zest.
BEAT the butter and sugar together using an electric mixer until pale and light.  Add the egg yolks one by one, then add the almond mixture and fold together.
PUT the ricotta into a bowl and beat lightly with a fork.  Add the lemon juice.
IN ANOTHER bowl, whisk the egg whites until they form soft peaks. Fold the egg whites into the almond mixture and finally stir in the ricotta.
SPOON the mixture into the prepared tin and bake in the oven for 40 – 50 minutes, until set.  Test by inserting a skewer, which should come out clean.  Leave in the tin to cool for 10 minutes before turning out.
DUST liberally with sifted icing sugar before serving.