Can this be made using some Brioche buns instead of the challah?, thanks

Croissants would work nicely too

It will probably taste even better made with brioche buns, given that they are full of butter, which makes any baked good taste fabulous. You also have a greater crust-to-crumb ratio with the buns which, to my mind, will also improve it. Either way, this sounds altogether delish! ;o)

Definitely!