Sauté onion in melted butter until tender. Add flour and blend. Slowly add milk, stirring constantly. Cook until thickened. Season with salt and pepper. (Or make the sauce of 1 can cream of chicken soup, adding ½ soup can of milk and the sautéed onion.)
Add salmon chunks, carrots, uncooked peas, and grated cheese. Pour into casserole. Top with rolled biscuit doug