In large skillet over medium heat, melt butter. Add garlic and cook for 1 minute; remove and discard garlic. Stir in breadcrumbs, coating well; stir in cheese. Set aside.
Bring large pot of water to boil. Cook cauliflower for 2 minutes; add broccoli and cook 4 minutes longer or until vegetables are tender-crisp. Drain well; transfer to 12 cup (3 L) casserole. Keep warm.
SAUCE: In large saucepan over medium-low heat, melt butter. Whisk in flour; cook, stirring until it changes colour slightly, 2 to 3 minutes. Gradually whisk in milk, increase heat to medium, whisking constantly until mixture comes to boil. Stir in cheese, onion powder and salt. Pour over hot vegetables. Top with reserved breadcrumb mixture.
Bake in 350°F (180°C) oven for 20 minutes until bubbling and topping is golden brown. (If made ahead and refrigerated, add 15 minutes to the baking time.)
1 Serving PROTEIN: 12 grams FAT: 12 grams CARBOHYDRATE: 22 grams CALORIES: 242 FIBRE: 3 grams SODIUM: 543 mg