1. Preheat oven to 350°F. Grease the bottom and sides of an 11 x 7 inch baking dish. Chop the onion. Heat butter in a small nonstick skillet over medium-high heat until melted. Saute until tender
2. Combine onion, chicken, soup, sour cream, milk, and pimiento in a medium bowl and mix well. Spoon mixture into prepared baking dish. Bake for 15 min. Remove from oven.
3. Sprinkle baked layer with 3/4 cup of the cheddar. Arrange biscuits in single layer over top. Sprinkle with remaining cheese. Bake until biscuits are golden brown and the sauce is bubbly about 20 minutes longer. Serve immediately.