potato gorgonzola gratin

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• 2 tablespoons butter
• 2 1/2 tablespoons all-purpose flour
• 1 teaspoon chopped fresh thyme
• 2 1/2 cups fat-free milk $
• 3/4 cup (3 ounces) crumbled Gorgonzola or other blue cheese
• 1 1/2 teaspoons salt
• 1/4 teaspoon freshly ground black pepper
• 3 pounds baking potatoes, peeled and cut into 1/8-inch-thick slices $
• Cooking spray $
• 1/3 cup (1 1/2 ounces) grated Parmigiano-Reggiano cheese

1. Preheat oven to 375°.
2. Melt butter in a small saucepan over medium-high heat. Add flour, and cook 2 minutes, stirring constantly with a whisk. Stir in the thyme. Gradually add milk, stirring with a whisk; cook over medium heat until slightly thick (about 3 minutes), stirring constantly. Stir in the Gorgonzola; cook 3 minutes or until cheese melts, stirring constantly. Stir in salt and pepper. Remove from heat.
3. Arrange one-fourth of potatoes in bottom of a 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 Parmigiano-Reggiano. Cover and bake at 375° for 30 minutes. Uncover and bake an additional 40 minutes or until potatoes are tender. Remove from oven; let stand 10 minutes before serving.