Potato Gorgonzola Gratin

2 tablespoons butter
2 ? tablespoons flour
1 teaspoon chopped thyme
2 ? cups skim milk
? cup (3 ounces) crumbled Gorgonzola
1 ? teaspoon salt
? teaspoon pepper
3 pounds baking potatoes, peeled and cut int 1/8 inch slices
2/3 cup (1 ? ounces) grated Parmesan cheese

Heat oven to 375.
Melt butter in small saucepan over medium high heat. Add four and cook two minutes, stirring constantly with a whisk. Stir in thyme. Gradually add milk, stirring with a whisk. Cook over medium heat about three minutes until slightly thick, stirring constantly.
Stir in the Gorgonzola and cook three minutes or until cheese melts, stirring constantly. Add salt and pepper and remove from heat.
Arrange one-fourth of potatoes in bottom of 13 x 9 inch baking dish coated with cooking spray. Spoon about 3/4 cup sauce over potatoes. Repeat layers twice, arrange remaining potatoes over sauce.
Sprinkle with Parmesan cheese and cover and bake at 375 for 30 minutes. Uncover and bake an additional 40 minutes or until potatoes are tender.
Let stand 10 minutes before serving.