Spray a 9x13 or similar casserole dish with olive oil.
Heat oil in a saute pan and start sautéing the mushrooms with 1/2 teaspoon salt and the Italian seasoning. Allow to cook at medium-high for 10 minutes.
Tear up the croissants and arrange two thirds of them in the prepared dish.
Tear apart the Boursin and tuck it around the bread and then sprinkle with 1/2 cup of the cheese and 1/2 of the mushroom mixture.
Add the remaining croissants and top with another 1/2 cup of the cheese and remaining mushrooms, leaving any juice from the mushrooms in the saute pan.
Whisk together the cream, milk, dijon, remaining salt and eggs. Pour the mixture over the croissants and top with remaining cheese.
Spray from aluminum foil with oil so it won't stick to the cheese, cover the dish and allow it to sit for 30 minutes before baking.
While it sits preheat the oven to 350.
Bake the dish covered for 40 minutes, remove the foil and bake 10-15 minutes longer. Remove from the oven, allow to rest 5-10 minutes and serve right away!