Two-Potato Casserole

In 5-quart saucepot over high heat, heat both kinds of potatoes, unpeeled, and enough water to cover to boiling. Reduce heat to low; cover and simmer until potatoes are just fork-tender but not soft, about 25 minutes; drain. Cool potatoes until easy to handle.

Meanwhile, thinly slice onions. In 10-inch skillet over medium-high heat, in 1 tablespoon hot salad oil, cook onions until tender and golden, stirring occasionally; set aside.

Peel and cut both kinds of potatoes into 1/4-inch-thick slices. Preheat oven to 350 degrees F.

Prepare sauce: In 2-quart saucepan over medium heat, in 3 tablespoons hot salad oil, cook flour, salt, and pepper 1 minute. Gradually stir in milk; cook, stirring constantly, until sauce thickens and just comes to a boil, 10 to 15 minutes.

In deep 2 1/2-quart round casserole, alternately layer one-third of both kinds of potatoes; top with half the onions, then one-third of the sauce. Top with half the remaining potatoes, all the remaining onions, and half the remaining sauce. Arrange remaining potatoes in casserole; top with remaining sauce.

Bake casserole 45 minutes or until gently bubbling and mixture is heated through. If you like, broil 1 to 2 minutes to brown top of potatoes slightly.