– Preheat oven to 180C (3750F). Butter a medium size casserole dish.
– Chop onion and mushrooms.
– In a preheated pan stir together chopped onions and mushrooms over a low heat until softened and slightly browned, about 5 minutes, sprinkle salt and pepper and set aside to cool.
– Prepare a white sauce: slightly grease with olive oil and preheat a pan, add flour and gradually whisk in heated milk in order to make a roux, and then cook under a gentle heat while stirring with a whisk. Cook until the souse thickened and smooth.
– In small bowl combine 4 tablespoons of olive oil, 3 spoons of mustard and a pinch of pepper to make a mustard sauce.
– Cut the chicken breast in slices, pound with meat mallet and season lightly with salt and pepper.
– Spread a thin layer of mushroom mixture and then the white sauce over each chicken breast.
– Place one slice of cheese and pastrami on top.
– Roll up a chicken breast starting from the thinnest end and place in a casserole dish.
– Spoon mustard sauce over top of each role and bake about 40-50 minutes.
– You can serve it with potatoes, pasta or rice.