Preheat the oven to 160°.
Line the bottom of a 7½ cm deep springform pan or other 30 cm cake tin with baking paper, and grease it.
Beat the butter and sugar until light and fluffy with an electric mixer.
Stir in the almond flour and vanilla.
Beat in the eggs one at a time.
Fold in the lemon zest and juice, followed by the polenta, baking powder, and salt.
Pour the batter into the prepared tin.
Bake the cake for 45-50 minutes, until fully baked and dark brown on top.
Let it cool in the tin.
In winter, we serve this cake with caramelized blood oranges and crème fraîche.