Preheat the oven to 350°. In a bowl, whisk egg whites with salt until stiff peaks form. Gradually stir in with a wooden spoon a little at a time the egg yolks, followed by the sugar, oil, milk, orange zest and ending with the sifted flour.
When all the ingredients are incorporated, half fill cupcake liners with batter and place on a large baking sheet.
Bake for 18 to 25 minutes until golden brown. Remove from the oven and transfer the cake in their baking cups to wore racks to cool.