In a Dutch oven cook corkscrew macaroni in lightly salted boiling water for 7 minutes. Add the frozen vegetables; return to boiling. Cook for 2 minutes more or until pasta is tender. Drain well.

In a screw-top jar combine flour, salt, pepper, nutmeg, dried herb (if using), and 1 cup of the milk; shake well. Transfer to a large saucepan; add remaining 2-1/2 cups milk. Cook and stir over medium-high heat until slightly thickened and bubbly. Gradually add cheeses, stirring until melted. Stir in cooked pasta and vegetables and fresh herb (if using). Transfer to a lightly greased 3-quart rectangular baking dish.

Bake, covered, in a 350 degree F oven for 25 minutes or until heated through. If desired, garnish with thinly sliced plum tomatoes and additional snipped fresh oregano or basil. Makes 8 cups (6 main-dish or 12 side-dish servings). Nutrition facts are given for side-dish servings.

Chill the unbaked casserole for up to 4 hours. Bake in a 350 degree F oven for 35 to 40 minutes or until heated through; stir before garnishing and serving.

Bake the casserole just before leaving home. Wrap the hot casserole in several layers of newspaper and a heavy towel; place the wrapped casserole in a large cardboard box or an insulated container to tote. It should stay warm for up to 2 hours. (Or, if making ahead, tote the chilled casserole in a cooler; bake the casserole once you arrive at your potluck site.)