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Preheat the oven to 400°. In a large saucepan, steam the cauliflower until just tender, about 7 minutes; let cool slightly. Cut the cauliflower into 1-inch pieces and spread evenly in a 10-by-15-inch shallow baking dish.
Heat the olive oil in a large skillet. Add the garlic and anchovies and cook over low heat until fragrant, about 2 minutes. Add the scallions and cook, stirring, until softened, about 1 minute. Add the chicken stock and boil over moderately high heat until reduced by half, about 5 minutes. Add the cream and simmer over low heat until reduced to 1 1/2 cups, about 4 minutes. Pour the cream over the cauliflower.
In a bowl, toss the bread crumbs with the cheese and melted butter. Season with salt and pepper and sprinkle over the cauliflower. Bake in the upper third of the oven for about 20 minutes, or until bubbling and golden. Let stand for up to 20 minutes before serving.
The recipe can be prepared through Step 2 and refrigerated overnight. Bring to room temperature before proceeding.