Salt, as needed
1 (3-pound) head cauliflower, cut into large florets
4 tablespoons butter, divided
1/2 cup finely chopped sweet onion
3 tablespoons all-purpose flour
1 cup half-and-half
1 cup chicken broth
1/2 teaspoon freshly ground black pepper
1/4 teaspoon grated nutmeg
1/2 cup freshly grated Parmesan
1 cup freshly grated extra-sharp cheddar, divided
1/3 cup fresh breadcrumbs
Preheat oven to 375 F.
Bring a large pot of salted water to a boil. Drop the cauliflower florets into boiling water and cook just until barely tender, about 6 minutes; drain well.
Meanwhile, melt 2 tablespoons of the butter in a medium saucepan over medium-high heat. Add the onion and saute until onion is soft and transparent. Reduce heat to low and whisk in the flour, stirring continuously for about 2 minutes.
Combine the half-and-half and chicken broth and heat in microwave or on stovetop until very hot. Whisk hot broth-cream mixture into flour over medium heat, stirring continuously until mixture comes to a boil. Continue whisking until thickened. Remove pan from heat and stir in the pepper, nutmeg, salt to taste, the Parmesan and 1/2 cup of the cheddar.
Pour one-third of sauce into bottom of a shallow, 8-by-11-inch baking dish (or gratin dish). Place drained cauliflower on top and spread remaining sauce evenly over top. Combine the breadcrumbs with remaining cheddar and sprinkle on top. Melt remaining butter and drizzle over top. Bake in preheated oven for 25 to 30 minutes, until top is nicely browned. Serve hot or at room temperature.
Makes about 6 servings.