Preheat oven to 170C/150C fan forced. Grease and line the base of a 20cm (base size) round springform cake pan with baking paper.
Use electric beaters to beat the butter, sugar and lemon rind in a bowl until pale and creamy. Gradually add the ricotta and beat until just combined. Add the eggs, one at a time, beating well after each addition (don’t worry if it looks curdled at this stage).
Add the flour, polenta, salt and lemon juice to the butter mixture. Use a large metal spoon to fold until just combined. Transfer mixture to the prepared pan and smooth the surface.
Bake for 45 minutes or until the cake springs back when lightly touched in the centre. (The cake will rise slightly but will sink back to a flat surface when cooling). Set aside in the pan for 10 minutes before transferring to a wire rack to cool completely. Dust with Icing Sugar to serve.
