Melt butter in heavy medium saucepan over medium heat. Add flour and whisk until mixture is smooth, about 1 minute. Whisk in milk and salt. Whisk until mixture thickens slightly, about 2 minutes. Gradually whisk in cheeses. Stir until mixture is smooth and begins to bubble, stirring, constantly, about 5 minutes. Cover and keep warm.
Egg Pastry Crowns Preparation:
Meanwhile, preheat oven to 400 degrees F. Line a cookie sheet with parchment paper.
Place 1 layer of pastry shells on the prepared cookie sheet and brush with egg wash. Top with another hollowed out shell. Bake for 12 minutes, or until golden on top.
Whisk eggs and milk in a large bowl to blend. Place a large nonstick skillet over medium heat. Add oil and butter to skillet. When the butter foams, add the egg mixture. Stir continuously with a rubber spatula until eggs are light and fluffy, about 2 minutes. Season, to taste, with salt and pepper. Remove tops and hollow out pastry shells. Divide scrambled eggs among pastries. Top each with 2 to 3 tablespoons of Mornay Sauce. Sprinkle with chives and serve.