In a bowl, use an electric hand mixer to beat the eggs with the sugar until light and frothy. Gradually add the milk, oil, orange juice and grated peel, mixing well. Incorporate the sifted flour a little at a time, then the cocoa and lastly the baking powder, both of which sifted as well. Stir thoroughly, and when everything is perfectly combined pour the mixture into the cake tin, which you have previously greased with butter and sifted with flour (shaking off the excess flour). Level the surface with a spatula and bake in a preheated oven, at 175 °C, for approximately 45 minutes. After 40 minutes, do the toothpick test: stick one into the centre of the cake, if it comes out dry it’s ready, if not cook for at least another 5 minutes. Let the cake cool down completely, remove it from the tin and sprinkle it with icing sugar. This cake can become even more delicious: cut it in half horizontally and spread the bottom part generously with pastry cream, chocolate spread (or Viallella), strawberry jam or orange marmalade (or whatever you prefer), then put the other half back on top and sprinkle with icing sugar.