Orange roll cake filled with chocolate

Directions

1. Preheat the oven to 180ºC (350ºF).
2. Separate the yolks from the whites. Beat the egg whites until stiff peaks form and reserve in the fridge.
3. In an electric mixer, beat on medium speed the egg yolks together with the sugar and the orange zest until obtain a very creamy mixture. Add the softened margarine and the orange juice and mix for 2 to 3 minutes until well incorporated. Reduce the mixer speed to low, add the flour mixed with the baking powder and beat until a homogeneous and creamy mixture. After everything well beaten, fold gently with a spatula the whipped egg whites.
4. Line a baking tray (36 x 30 centimeters (14 1/4 x 11 3/4 inches)) with butter and parchment paper and spread the dough over the top with the help of a spatula. Bake for about 15 minutes until slightly golden (the time depends on the oven).
5. When the cake is cooked, remove from oven and sprinkle the cake with sugar. Place a tea towel over top and flip the cake over the table. Remove the tray and peel carefully the parchment paper. Cut with a knife the edges of the cake. Using the towel, start rolling the cake gently from one short end to the other; set aside.
6. For the filling:
   Place the chocolate broken into pieces in a bowl and melt in the microwave.
7. In an electric mixer, beat on medium speed the powdered sugar and the the softened margarine until obtain a creamy and homogeneous texture. Then, add the melted chocolate, without stop beating.
8. Unroll the cake and spread the filling with a spatula. Then, re-roll slowly to not break the cake (remove the towel as you rolling). Place the roll cake on a rectangular plate and serve.