Separate 4 egg yolks from 4 egg whites in two different bowls. Set aside the egg whites.
Gradually add the sunflower oil into the yolks while whisking with handheld on medium speed, until the mixture absorbs the oil.
Now gradually add the sunflower oil to the yolks while whisking with hand mixer at medium speed.
With two oranges, grate the peel of one orange and set aside it´s zest; then, squeeze the two oranges to make juice, and add it little by little into the yolk mixture with the handheld on medium speed until combined.
In a third bowl, mix flour, salt and powder. Add a third of this mixture to the strainer, sift over the yolk while beating with the handheld on medium speed. Repeat this process up to three times.
Now add the grated orange zest to the batter, and whisk on medium speed.
Beat the egg whites until stiff. Then, add into the batter with a spatula making folding movements from bottom to top.
Pour the batter into a 8 inch cake pan. The pan has previously been buttered and floured so that the batter does not stick. Another option is to line the cake pan with parchment paper.
Bake for 45 minutes.
When the cake is ready, unmold it and let it cool on a wire rack. When it has completely cooled, cut it into three parts and fill each layer with dulce de leche.
Whip together cream and sugar with the hand held mixer until soft peaks. Then, cover the cake with the whipped cream… Et voilà! You have a delicious birthday cake with dulce de leche!