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1
Preheat oven to 425 F. In a small casserole dish (1 1/2 to 2 1/2 quarts), toss broccoli pieces with the olive oil, then sprinkle with 1/4 teaspoon salt and a pinch of pepper.
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2
Roast in the bottom third of the oven for 5 minutes, until just tender with some crunch in the middle.
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3
Remove from oven.
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4
Keep the oven on but reduce temperature to 375 F.
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5
While broccoli cools, make the sauce.
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6
Scald the milk in a small saucepan by heating it over medium until tiny bubbles form around the edges.
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7
Remove from heat and cover the pan to keep milk warm.
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8
Have broth ready and close to room temperature.
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9
Melt the butter over medium heat in a medium saucepan, then add onions and cook until softened, 4 to 5 minutes.
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10
Add flour and mustard powder and stir constantly with a wooden spoon for 3 to 4 minutes.
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11
Turn off heat.
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12
Slowly whisk in the hot milk until incorporated (no need to rush here), then whisk in the broth.
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13
Increase heat to medium high so the sauce comes to a simmer (turn down heat if it starts to simmer really rapidly), then simmer, stirring constantly with a wooden spoon or spatula, until thickened, about 8 to 10 minutes.
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14
When sauce is done, turn off heat and stir in celery, 1 teaspoon salt (or more to taste), and pepper to taste.
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15
Mix broccoli and rice together in the casserole dish used to roast the broccoli.
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16
Pour sauce over the mixture then stir to incorporate.
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17
Top with grated cheddar.
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18
Bake at 375 F on the middle rack for 20 to 25 minutes, until cheese is melted.
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19
Then turn on the broiler and broil the cheese for a few minutes to brown it, if desired.
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20
Remove from oven.
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21
Let it stand for a couple minutes, but serve hot so the cheese doesnt firm up.
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22
Note: Cook time includes 25 minutes to cook the rice.
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23
If made in advance, total time for this recipe will be much shorter.
