2 lbs. Yukon Gold potatoes , peeled and very thinly sliced (about 3 mm-thick)
2 Tbsp. plain dry bread crumbs
Preheat oven to 375°F (190°C). Melt Becel® Buttery Taste margarine* in 3-quart saucepan over medium-high heat and cook onion, stirring occasionally, 5 minutes or until starting to brown. Add garlic and cook 30 seconds. Stir in flour and cook, stirring constantly, 1 minute. Whisk in milk gradually. Add broth and bring to a boil. Stir in thyme and black pepper. Remove from heat, then stir in 125 g cheese; set aside.
Lightly spray 33 x 23 cm shallow casserole with no-stick cooking spray. Arrange ½ of the potatoes in overlapping pattern in casserole. Stir cheese mixture, then pour 1/2 over potatoes. Repeat with remaining potatoes and cheese mixture.
Bake uncovered 45 minutes. Combine remaining cheese with bread crumbs; sprinkle over potatoes. Bake an additional 10 minutes or until potatoes are tender and top is golden brown.