This is another favorite from House & Garden.

Walnut-Sage Potatoes au Gratin

6 medium potatoes (2 lb.)
1/2 cup chopped onion
2 cloves garlic, minced
3 Tbsp. walnut oil
3 Tbsp. all-purpose flour
1/2 tsp. salt
1/4 tsp. pepper
2 1/2 cups milk
3 Tbsp. snipped fresh sage
4 oz. Gruyere cheese, shredded (1 cup)
1/3 cup broken walnut pieces
Fresh sage leaves (optional)

Peel potatoes, if desired, and thinly slice (should have 6 cups). Place slices in a colander. Rinse with cool water; set aside to drain. For sauce, in a medium saucepan cook onion and garlic in walnut oil until tender but not brown. Stir in flour, salt, and pepper. Add milk all at once. Cook and stir over medium heat until thickened and bubbly. Remove from heat; stir in snipped sage. Grease a 2-quart round casserole (with glass cover). Layer half of the potatoes in casserole. Cover with half the sauce. Sprinkle with half the cheese. Repeat layering with the potatoes and sauce. (Cover and chill remaining cheese until needed.) Standard oven method: Bake casserole, covered, in conventional oven at 350 degrees F for 40 minutes. Uncover; bake 25 minutes more or until potatoes are just tender. Sprinkle remaining cheese and nuts over top. Bake, uncovered, 5 minutes. Let stand 10 minutes. Top with sage leaves. Microwave method: Using a microwave-safe casserole, assemble ingredients through Step 3. Cover with plastic wrap, turning back an edge of wrap to allow steam to escape. Microcook on 70% power (medium-high) for 25 to 30 minutes or until potatoes are tender. Uncover; sprinkle remaining cheese and walnuts over top. Cover and let stand 5 minutes. Top with sage leaves.