Baked Brussels Sprouts Gratin

Bahan-bahan (8 porsi)

• 2 pounds Brussels sprouts (halved lengthwise, quartered if large)
• 1 tablespoon olive oil
• salt and pepper to taste
• ⅔ cup heavy whipping cream
• ¼ teaspoon onion powder
• 1 ⅓ cups shredded sharp cheddar cheese (divided)
• ¼ cup shredded Parmesan cheese