Preheat the oven to 180 º C.
Beat the yolks with the sugars until you have a paler mixture.
Add the Port wine and cinnamon. Mix a little more.
In a food processor, blitz 200 g of walnuts to get a flour-like consistency. Coarsely chop the remaining nuts with a knife.
Add the walnuts to the mixture and beat once more.
In the mixer, beat the egg whites to stiff peaks.
Carefully fold the egg whites into the mixture, without overmixing.
Spread the cake batter in a rectangular cake pan (mine is about 28 x 15 cm), previously greased.
Bake for about 35 to 40 minutes, or until a skewer inserted in the center of the cake comes out dry.
Let the cake cool down for a few minutes, then unmold on a serving plate.