Preheat the oven at 180 degrees Celsius.
Melt the butter and sugar in a casserole and pour it in a baking bowl.
Add the baking powder, flour, egg yellow and the orange blossom water and stir well.
Mix the egg white to a hard foam, add gently to the batter.
Butter a baking form and pour the batter in.
Place the cake in the middle of the oven for forty minutes.
Take out the cake and let it cool down.