6 medium potatoes (2-1/2 to 3 lbs.) 2 medium onions, sliced 1/4 cup (50 mL) butter or margarine 2 tablespoons (30 mL) all-purpose flour 1-1/2 cups (375 mL) chicken broth (homemade or canned) salt and black pepper to taste 2 cups (500 mL) fresh bread crumbs (coarse)
Preheat the oven to 350°F (180°C). Grease a 9×13-inch (23×33-cm) rectangular baking dish.
Scrub potatoes well and slice them very thinly (1/8 inch or 0.25 cm thick). It is not necessary to peel the potatoes, unless you prefer to do so. Place them in a bowl of cold water and set aside.
In a medium skillet, sauté sliced onions in 2 tablespoons (30 mL) of butter or margarine over low heat until evenly golden, 10 to 15 minutes. Set aside.
In a small saucepan, melt together the remaining 2 tablespoons (30 mL) of the butter or margarine and the flour over medium heat. Whisk in chicken broth, stirring constantly until the sauce thickens and bubbles. Continue to simmer for a minute or two, then remove from heat. Season to taste with salt and pepper.
Drain potatoes completely and layer them as follows: 1/3 of the potatoes, 1/2 of the onions, salt and pepper; 1/3 of the potatoes, remaining onions, salt and pepper; and finally all the remaining potatoes. Pour the sauce evenly over the potatoes and cover the baking dish tightly with foil. Bake for 45 minutes. Remove foil, sprinkle with bread crumbs and continue baking for an additional 45 minutes or until potatoes are tender and crumbs are crisp and browned.