how to create gratin with _thin_ cheese skin

I would think all of the above will give tasty results, the point about the use of a professional broiler or salamander is possibly the real clue for cheese to crisp it needs heat, the rest of the dish probably does not.

There are a few tricks to try,

1 use any of the above mixes but get yourself a blow lamp from the DIY store or garage, not a silly little overly priced armature cook shop one, and use it to flame the tops just before serving(warn guests of the temperature before they burn their mouths) Effectively same as a good crème brulee.

2 make parmigiana disks grate parmigiana very finely on to a silicon tray or baking sheet oven roast until crispy or use grill if you have a hot broiler. let them cool on a rack place them on top at the end of the cooking - Combine with the blow lamp to colour and heat as a professional touch.

3 the lazy way add a dash of butter to the tops during the baking to colour the cheese mixture.

I think this can be done very easy:
- you can put parmesan into your sauce but this won't color in the oven.
- just before placing it in the oven, add a good layer of grated cheese (young cheese)
- when the dish is almost ready, place it for max 1 minute under the grill in the oven. (until it colors).
NOTE, this will go very fast so keep an eye on it.

Enjoy:)

I never tried it but I would go about this using another cheese, like provolone, and instead of grating I would use fine flakes.

An a max oven + grill.

I make mine with a bechamel sauce and just use cheddar. It is slightly thick but not too thick. Also cook in a hot oven 400 degrees, this gets a nice thin skin on it every time! Good luck!