Cauliflower and Leek Gratin

This scratches the itch when I crave mac and cheese, but still want to eat my veggies.  You can play with various cheeses to get different flavors.  Tonight its gruyere and an aged gouda.

Roasted Cauliflower & Leek Gratin

Roasting the leeks and cauliflower (which you can do well ahead) brings out deeper flavor and a crisp-around-the edges texture. Serve as a side dish with roasted meat, or as a main course with salad and bread. If you don't feel like making the white sauce, gently warm 1 1/2 cups of cream in a saucepan until bubbles form around the edges, then stir in the cheese and season with salt and pepper. Pour it over the vegetables.

• Roasted vegetables
• 2 small heads cauliflower, about 3 pounds untrimmed
• 4 tablespoons olive oil
• -- Kosher salt and pepper to taste
• 3 cloves garlic, minced
• 1 large leek
• Gratin
• 1 1/2 tablespoons butter
• 1 1/2 tablespoons flour
• 2 cups low-fat milk
• 1/2 cup (generous) grated Parmesan, gruyere or Manchego cheese
• -- Kosher salt and white or black pepper
• 1 teaspoon whole-grain Dijon mustard
• 1 to 2 ounces ham, cut into baton shapes (optional)
• 1/4 cup breadcrumbs

To make the roasted vegetables: Preheat the oven to 400°.
Cut the cauliflower into florets that are 1 1/2 inches wide. In a large bowl, toss the florets with 3 tablespoons olive oil. Season with salt and pepper, and spread out on a large rimmed baking sheet. Roast until tender with just a bit of bite and browned, 35-40 minutes, stirring occasionally. Stir in the garlic after 20 minutes.
Meanwhile, remove the coarse dark tops of the leek and cut lengthwise. Wash thoroughly, then cut each half into 2-inch lengths, discarding any more dark green ends and checking for hidden dirt.
Separate the layers and toss with the remaining 1 tablespoon oil and some salt, then spread out on another large rimmed baking sheet and roast until crispy in some parts and thoroughly soft throughout, about 15 minutes. (You can roast the vegetables several hours ahead and refrigerate before completing the dish.)

To make the gratin: In a medium saucepan, melt the butter over medium-low heat. Whisk in the flour and cook, stirring constantly, for 3-5 minutes, taking care that it doesn't brown. Whisk in the milk until smooth, then bring to a simmer. Maintain the heat so it's bubbling gently; stir often until the sauce thickens and the flour cooks, about 15 minutes. Add 1/3 cup of the Parmesan and stir until just melted. Remove from the heat and season well with salt and pepper, then stir in the mustard.