Photograph: Martin Poole
Preheat the oven to 180°C, fan 160°C, gas 4. Lightly grease a 22cm springform cake tin and line with baking paper. Whiz the pistachios in a food processor or blender until finely ground.
In a large bowl, cream the butter and sugar until light and fluffy. Gradually add the eggs, mixing well after each addition.
In another bowl, mix the polenta, ground almonds, pistachios and baking powder. Add this to the butter, egg and sugar mixture and mix well. Stir in the lemon zest and juice and mix until combined.
Pour the mixture into the cake tin, level the top and bake for 45-50 minutes or until golden and firm to the touch. Cover the top of the cake with foil after 30 minutes to stop it browning too much.
To make the syrup, in a small pan bring the lemon zest and juice and caster sugar to the boil, stirring to dissolve the sugar. Reduce the heat and simmer for 3 minutes. As soon as the cake is out of the oven, pour the hot syrup over it, then leave to cool in the tin.
Get ahead: can be made up to 3 days ahead; it also freezes well.
Kitchen secret: this deliciously moist cake can be made well ahead – the flavour only improves. It is also lovely with sliced oranges, drizzled with a little honey.