Roasted Cauliflower Gratin

ingredients

2 medium cauliflower heads (about 10 cups, 20 ounces florets)
2 tablespoons olive oil for drizzling
1/2 teaspoon salt
½ teaspoon pepper
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2 Tablespoon olive oil or butter
1 onion, diced or sub 2 fat shallots)
6–8 garlic cloves, rough chopped
2 tablespoons fresh chopped sage (or 2 teaspoons dry sage, or sub rosemary or thyme)
Bechamel Sauce:

2 tablespoons butter
3 tablespoons all-purpose flour (or gf flour)
2 cups milk, hot
1/2 teaspoon kosher salt
1/4 teaspoon white pepper
1/4 teaspoon nutmeg (fresh grated is nice)
¼ cup grated gruyere cheese- (or mozzarella -plus 3 Tablespoons for the top)
¼ cup grated Parmesan or pecorino
Optional Additions:

¼ cup crispy bacon bits, or crispy pancetta
¼ cup vegan “bacon bits”
bread crumb topping (see notes)
instructions
Preheat oven to 400 F.
Roast the Cauliflower: Cut cauliflower into bite size pieces, toss with olive oil (just enough to lightly coat) salt and pepper and place on one (or two) parchment-lined sheet pans ( in a single layer) and bake until tender and golden, about 20-25 minutes.
Saute the onions: In an extra large skillet saute the onion over med- high heat in olive oil until tender and fragrant, stirring often, about 3-4 minutes. Add garlic and sage and lower heat to medium and sauté 3-4 minutes, until fragrant, season with salt and pepper. Take your time here and make sure onion and garlic are golden and tender. Set aside.
Make the Bechamel Sauce: In a small pot, melt butter over medium heat. Stir until butter just begins to become golden and becomes nutty and fragrant. Add flour. Stir and cook flour for at least 1 minute. Whisk in ½ C hot milk making sure to whisk all the flour from the corners and sides of the pot. Add another ½ C milk, whisking well. Add the final cup of milk, nutmeg, salt and pepper and whisk constantly until mixture thickens and just comes to a simmer. Turn heat to low and whisk in cheese and set aside.
Assemble: Use a greased, oven-proof 10 inch cast iron skillet, 8×11 inch baking dish or greased individual ramekins. Toss the roasted cauliflower with the Bechamel sauce and onions/garlic/ sage mixture. Taste for salt and pepper, adjusting to your liking.
Top with optional bread crumbs (see notes), optional crispy bacon or pancetta (or vegan bacon bits) a few sage leaves or a little more cheese. You could refrigerate this overnight at this point if making ahead (perhaps not in the cast iron). If refrigerating, be sure to bring to room temp before baking.
Lower heat to 375 F and bake uncovered in the oven, until golden and bubbly, about 20-25 minutes.