Ingredients

• 2 1/2 cups cauliflower florets
• 2 1/2 cups broccoli florets
• 2 6-ounce bags baby spinach leaves
• 6 tablespoons (3/4 stick) butter
• 1/4 cup all purpose flour
• 2/3 cup whole milk
• 2/3 cup freshly grated Parmesan cheese

Instructions

1. Cook cauliflower and broccoli in large pot of boiling salted water until crisp-tender, about 5 minutes. Drain, reserving 2/3 cup cooking liquid. Transfer vegetables to large bowl. Cool.
2. Rinse spinach, then toss in large nonstick skillet over medium-high heat until just wilted. Drain and cool. Squeeze spinach dry; finely chop.
3. Melt butter in heavy medium saucepan over medium heat. Add flour and whisk until smooth, about 2 minutes. Gradually whisk in milk and reserved 2/3 cup vegetable cooking liquid. Whisk constantly over medium heat until sauce thickens and boils, about 3 minutes. Stir in spinach and cheese.
4. Using fingers, coarsely crumble cauliflower and broccoli in bowl. Add spinach béchamel sauce; stir to blend. Season with salt and pepper. Butter 1 1/2-quart baking dish. Spread vegetable mixture in prepared dish. (Can be made 6 hours ahead. Cover and chill.)
5. Preheat oven to 350°F. Bake flan until puffed and heated through, about 25 minutes if at room temperature and 35 minutes if chilled. Serve hot.