2 tablespoons unsalted butter
2 tablespoons all-purpose flour
2 cups 1-percent milk
Coarse salt and freshly ground pepper, to taste
2/3 cup (2 ounces) grated smoked Gouda cheese
1 tablespoon canola oil
1 bag (12 to 16 ounces) frozen pearl onions
1 1/2 pounds Brussels sprouts
2/3 cup (2 ounces) finely grated aged Gouda
2/3 cup panko breadcrumbs or fresh breadcrumbs
Smoked, flaked sea salt, optional, or regular sea salt
Preheat oven to 375 F.
In a saucepan, melt the butter over medium heat. Add the flour and whisk until mixture bubbles slightly but has not started to brown, about 2 minutes. Gradually whisk in the milk. Raise heat to medium high and bring to a boil, whisking often. Reduce heat to low and cook, stirring occasionally with a wooden spoon, until thickened, 12 to 15 minutes. Season with the coarse salt and pepper. Remove from heat. Add the smoked Gouda and stir until melted. (May make bechamel up to 4 days in advance; cover and keep refrigerated.)
Meanwhile, heat the oil in a skillet over medium heat, add the pearl onions and saute for 5 minutes until lightly brown.
Bring a medium pot of salted water to a boil. Cook the Brussels sprouts until just tender when pierced with tip of a paring knife, 3 to 4 minutes. Drain and transfer to an 8-cup (8-by-12-inch) baking dish. (May blanch and cool Brussels sprouts ahead and refrigerate up to 1 day.)
Mix Brussels sprouts and onions in baking dish. Pour bechamel over vegetables and sprinkle with the aged Gouda, panko breadcrumbs and a pinch of smoked sea salt. (Assembled gratin can be refrigerated overnight. Bring to room temperature before baking.)
Bake, uncovered, in preheated oven until bubbling and golden, about 25 minutes. Makes 8 servings.
— Recipe adapted by the Detroit Free Press from Martha Stewart Living magazine, December 2011.