This is a dish that has become a Thanksgiving tradition in my family. It was invented by my mom who was trying to sneak some healthy veggies into the meal without sacrificing decadence. I added the gruyere years later because I think it is the best melting cheese in the world, and it gives it a little more depth of flavor. I have also traded out the broccoli for celery root in the past but found that I missed the little pop of green the broccoli adds to the dish. A great potluck staple! —Brita
Preheat oven to 375°F. Fill a large bowl with ice water. Blanch Cauliflower and broccoli in a large pot of salted, boiling water until crisp tender (about 5 minutes). Drain and transfer veggies to ice water. Once cool, drain and set aside.
Combine cream and shallots in large saucepan. Bring to boil. Reduce heat; simmer until mixture is thickened, about 10 minutes. Season with salt and nutmeg. Remove from heat.
Heat oil and butter in large nonstick skillet over medium heat. Add breadcrumbs; stir until beginning to brown, about 2 minutes. Transfer to bowl to cool. Toast pine nuts in a dry pan over medium heat, watch carefully so they don't burn- about 2 minutes. Stir in pine nuts and parsley. (reserve some chopped parsley for garnish) Season with salt and pepper.
Butter a baking dish; arrange half of vegetables in dish. Sprinkle with salt and pepper, then 1 cups Parmesan and 1 cup gruyere. Arrange remaining vegetables evenly over, then sprinkle with remaining 1/2 cup parmesan and gruyere. Pour cream mixture evenly over.
Cover gratin with foil. Bake covered for 40 minutes. Uncover; sprinkle breadcrumb topping over and bake uncovered 15 minutes longer until browned. Top with fresh parsley garnish and serve.