Heat oven to 375°F. Combine Cream Sauce Base, broth, onion, salt and pepper in saucepan. Cook over low heat, stirring constantly, until bubbles appear around edges and mixture is thickened; 4 to 5 minutes.
Layer half of potatoes in half hotel pan that has been sprayed with nonstick cooking spray. Sprinkle with 2 ounces Monterey Jack cheese and 2 ounces Cheddar cheese. Cover with remaining potatoes.
Pour hot cream sauce mixture over potatoes; cover. Bake for 50 to 60 minutes or until potatoes are almost tender when pierced with fork. Uncover; top with remaining cheeses. Continue baking for 15 minutes or until potatoes are tender and cheese is melted.