Preheat the oven to 170C.
Cut and grease with butter, a piece of baking paper to fit in the bottom of a loaf tin.
Then butter the sides of the loaf tin and dust with the 2 tsp of flour.
Cream the butter and sugar together in a large mixing bowl until light and creamy.
Beat in the eggs and then add the lemon zest and juice.
Beat until well incorporated.
Carefully fold the Polenta, ground almonds and baking powder into the mixture.
Pour the cake mixture into the tin and bake in the centre of the oven for about an hour.
Check the cake after 30 minutes and, if it is becoming too brown, place a piece of baking paper loosely over the top.
Check to see if the cake is cooked by inserting a skewer into the centre of the cake – it should come out clean.
Remove from the oven and leave to cool for 10 – 15 minutes before removing from the tin.