Preheat oven to 180 degrees C (350 degrees F). Line a 18-20 cm (7-8 inch) cake pan with a circle of baking paper and then grease well the pan.
In a bowl combine ground walnuts and flour and set aside.
In a mixing bowl using an electric mixer beat egg yolks, sugar and vanilla until thick and pale. Gradually add the dry ingredients and the milk, folding gently with a rubber spatula until well combined.
Wash and wipe the beaters of the mixer before beating the egg whites.
In another large bowl beat the whites with a pinch of salt until soft peaks form. Using a rubber spatula little by little add the egg whites to the yolk mixture. Fold gently until uniform.
Transfer the batter into the prepared pan and smooth the top with the spatula if needed. Bake for 40-45 minutes or until a wooden skewer inserted in the centre comes out clean.
Let the cake cool until room temperature before assembling it.