Heat oven to 350°F. Grease 1 1/2-quart casserole. In greased casserole, combine 1 cup of the cheese, sour cream, soup, thyme and pepper; mix well. Stir in potatoes and onions; cover. Bake at 350°F. for 45 minutes.
In small bowl, combine crushed croutons and remaining 1/4 cup cheese. Uncover casserole; sprinkle with crouton mixture. Bake uncovered for an additional 10 to 15 minutes or until bubbly and golden brown.