Preheat the oven to 180°C (350 degrees F) and line a muffin tray with 10 cupcake liners.
In a bowl, mix together the oil, melted butter, half of the sugar (50g), salt and vanilla.
Combine the flour with baking powder.
Add the flour and milk to the mixture and stir just until well combined, with no dry flour spots. Don't over-mix as that creates gluten and tough cupcakes.
In another bowl, mix the egg-whites on low speed until bubbles start to appear. Then increase the speed to medium-high and start adding the other half of the sugar (50 g) tablespoon by tablespoon, mixing well between each addition. Stop when the egg whites reach stiff peaks that hold its shape.
Take 1/3 of the egg whites and mix it with the cupcake batter.
Add the rest of the egg whites and gently fold them into the batter with a spatula to keep as much air as possible.
Distribute the batter to 10 cupcake liners and bake for 17-20 minutes. Check if the cupcakes are done by inserting a toothpick (or a knife) into the center of the cupcake, if the toothpick comes out clean with no wet batter on, it's done.
Take the cupcakes out of the oven and let them cool.