Begin by pre-heating your oven to 160°C. Organise a 20cm round cake tin, by greasing with butter & lining with baking paper.
Place your soft butter in a bowl & with an electric mixer on high begin to cream the butter & 1 cup of the caster sugar together. Do this by gradually adding the caster sugar to the mix & as it combines with butter it should dissolve & begin to turn pale, thick & creamy.
Once the butter & sugar have creamed together & have turned pale add your vanilla extract & lemon zest.
Add 1 egg yolk to the mix at a time, as it combines with the mixture, add the next until they have all been combined.
Fold the ricotta cheese by hand to the mixture. Once combined, then fold the almond meal into the mixture.
In a separate bowl, beat the reserved egg whites with an electric mixer on high until soft peaks begin to form. Gradually add the remaining 1/3 cup of caster sugar to the egg whites until it dissolves & stiff peaks begin to form.
Slowly by hand, fold the egg white mixture into the cake mixture until they are combined evenly.
Empty the cake mixture into the cake tin you prepared earlier & smooth the top so it is even. Decorate the top with Almond flakes & place in the oven for 40-45 mins. Once cooked it will be firm to touch & a skewer should come out clean from the centre. Once cooked, allow the cake to cool completely in the tin.