Step 1

Heat the oven to 350 degrees and butter a deep 9-by-13-inch baking dish.

Step 2

Bring a large pot of salted water to a boil. Add the broccoli florets and cook for 2 to 3 minutes, until bright green. Drain immediately and set aside.

Step 3

In a large heavy-bottomed pot, melt the butter with 1 teaspoon red-pepper flakes over medium heat. When melted, add the scallions, 1 teaspoon salt and the black pepper, and cook until scallions have softened, 3 to 4 minutes. Add the flour and stir to combine. Stir constantly for 1 to 2 minutes, until the flour streaks are slightly golden in color, then add the milk in a slow stream, stirring continuously.

Step 4

Continue to stir the milk until the mixture is thick and creamy, 6 to 8 minutes. Remove from heat and add 4 cups of the cheese, stirring vigorously to melt it down into a smooth sauce. Taste and season with salt.

Step 5

Add the cooked rice and parboiled broccoli to the pot and stir until evenly coated with sauce.

Step 6

Transfer the mixture to the prepared dish and sprinkle with remaining 1 cup grated cheese, Ritz crackers and remaining 1/2 teaspoon red-pepper flakes.

Step 7

Bake for 25 to 30 minutes, until bubbling. For more color, cook under the broiler for 2 to 3 minutes, watching carefully. Serve warm.