In a large bowl, mix the egg yolk and milk together.
Add the flour and the baking powder and mix. Set the mixture aside.
In a mixer bowl or using an electric whisk, beat the egg whites until stiff. When they start to foam, add the caster sugar a little at a time to make a meringue.
Using a flexible spatula, fold the meringue into the first mixture, taking care not to beat the air out of the egg whites. When your mixture is smooth and foamy, it is ready.
Heat a crêpe pan. Oil the surface using a sheet of kitchen roll dipped in oil. Add a large spoonful of batter to the hot pan. Lower the heat to cook your pancakes. If your pan is too hot, they will colour too quickly and the middle will not be cooked. Adjust the heat as you cook the pancakes. Allow 2 to 3 minutes per side.
Place on a wire rack after cooking to cool. Enjoy!