How can you achieve the glazed top in a mille-feuille? A mille-feuille (or tompouce) is a pastry, consisting of layers of puff pastry with pastry cream in-between (see this if you don't know it). 

If you buy it in a pastry store, I find that the glazed top is unique for this pastry. Recipes online tell me that it's confectioner sugar and egg whites, but I think it's something else. It's solid, yet soft. You can see your tooth print in it. It's white and sweet. I can't exactly explain how it differs from regular egg white/sugar icing, but in my opinion it does. 

Does anybody have a clue what I'm talking about? Do you know what's in it? Or is it just a basic egg white/sugar icing, and is my mind playing tricks on me?
The dessert discribed is not truley a "Tom Pouce", that is a different pastry.  What is discribed in the question is a "Napoleon" dessert pastry.  The Mille Feuille or Puff Pastry is topped with an icing called "Fondant".  Fondant in it's simplest (shortcut) form is made by mixed powdered sugar and water until the desired thickness is reached.  Some time in the open air will harden it a little further beacause of the water drying out.  Fondant made correctly is by making a simple syrup (water and sugar cooked together), cooking it to the "soft ball" stage or temperature of simple syrup, then dispursing it onto a marble slab (to cool it quickly) and with 2 baker knives (one in each hand) fold and kneed the sugar until it frosts from transluscent color to the frosty and shyny white color.  This is an old skill which has been taken over by machines.  Fontdant is now purchased from larger makers in 5 gal. buckets for a cost of appr. $25.00.