The big air holes are caused by mixing too hard and getting too many air bubbles, so mix gently. Another way to minimize the air holes is to let the batter sit for a longer period of time after it's done, which will also help.

In addition to the baking powder can not be added, do not add baking powder, Madeleine unique "little belly" protrusion will not be formed, and baking powder will make Madeleine fluffy.

The dryness of the Madeleines may be due to your oven temperature being too high or the baking time being too long, so it is recommended that you make some adjustments.

I hope the advice of a professional school teacher can help you.