Sift flour and cocoa powder together twice. Set aside.
Cream the butter and half of the sugar together until light and fluffy. Gradually add the egg yolks and beat well.
Mix in the sifted flour, cocoa powder, oil and almond flour.
Whip the egg whites to soft peaks, then gradually add the remaining sugar and continue whipping until stiff, glossy peaks form. Lighten the batter by folding in approximately one-quarter of the egg whites, then fold in the remaining whites.
Divide batter into a sheet pan and bake at 180°C until set