Tortellini in Parmesan Cheese Sauce

1 (16 ounce) package frozen cheese tortellini
1/3 cup butter or margarine
1 teaspoon flour
1/2 cup milk
1/2 cup grated Parmesan, mozzarella,
    Romano or Monterey Jack cheese
2 tablespoons chopped fresh parsley (optional)

Cook tortellini according to package directions; drain. Meanwhile, for sauce, heat milk in a medium saucepan.

While milk is heating, melt butter in a separate bowl in microwave. Stir flour and butter together. Add mixture to milk; cook and stir until slightly thickened and bubbly.