Mix the softened butter with sugar and vanilla sugar until smooth. Gradually add the eggs and stir for at least 5 minutes until creamy. Mix the flour, cornstarch and baking powder in a bowl and stir into the cream with a spoonful. Add the pinch of salt and stir the batter with the milk and rum until smooth.
Then spread the dough evenly in a rodon cake tin coated with margarine and sprinkled with breadcrumbs.
Put in the cold stove, switch to 160 ° C hot air and bake on the middle rack for 50 minutes.
Immediately afterwards loosen the edge with a knife and turn out onto a large plate.