Creamed Chicken Casserole

Why I Love This Recipe
This dish is delicious! Very filling and my family loved it! There was a richness to it but still amazingly good! Recipe posted by hdmacwa.
NOTE: This is RICH! You may sub sour cream for the mayo if you wish (hdmacwa)
Ingredients You'll Need
1 small onion
1 1/2 teaspoons butter
2 lbs chopped cooked chicken breasts or boneless skinless chicken thighs
1 (10 3/4 ounce) can cream of chicken soup
1 cup mayonnaise (I used 1/2 cup mayo, 1/2 cup sour cream)
1/2 cup milk
1/2 cup chopped pimiento or sauteed red bell peppers (I used sweet red bell pepper)
1 1/2 cups shredded mild cheddar cheese
refrigerated biscuits or croissants or dinner rolls (I used Big Buttery crescent rolls, 6 to a can)
Directions
Preheat oven to 350.
Spray the bottom and sides of an 11x7 inch baking dish or 10 inch quiche dish.
Chop the onion.
Heat butter in a small nonstick skillet and sautee until tender.
Combine cooked onion, soup, chicken, milk, pimiento, and mayo in a bowl and then turn into the prepared baking dish.
Bake for 15 minutes and remove from oven.
Sprinkle 1 cup of the cheese over the baked mixture.
Arrange biscuits or croissants (croissants are better!) decoratively in a single layer and sprinkle remaining 1/2 cup cheese over them.
Return casserole to oven and bake until biscuits are golden brown and sauce is bubbly, usually about 20 minutes longer.