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1
Melt 2 tablespoons butter in a large skillet over medium heat.
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2
Add onion, and cook, stirring occasionally, until beginning to soften, about 4 minutes.
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3
Add bell pepper and mushrooms, and cook, stirring occasionally, until softened and most of the liquid has evaporated, 8 to 10 minutes.
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4
Season with 1 teaspoon salt and 1/4 teaspoon black pepper.
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5
Remove from heat.
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6
Let cool completely.
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7
Bring a medium saucepan of water to a boil.
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8
Add beans; cook until bright green and just tender, 4 to 5 minutes.
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9
Drain, and plunge into an ice-water bath to stop cooking.
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10
Drain beans, and dry.
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11
Toss with mushroom mixture; set aside.
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12
Melt the remaining 4 tablespoons butter in a medium saucepan over medium heat.
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13
Add 1/4 cup flour; whisk constantly until mixture begins to turn golden, about 2 minutes.
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14
Pour in milk; continue whisking until mixture thickens, 4 to 6 minutes.
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15
Stir in cayenne, nutmeg, and remaining teaspoon salt and 1/4 teaspoon black pepper.
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16
Remove from heat; let cool completely, stirring occasionally.
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17
Pour over bean mixture, and toss.
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18
Butter a 13 x 9-inch baking dish.
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19
Spread half of the bean mixture into dish.
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20
Sprinkle with half of the Parmesan, and then top with remaining bean mixture.
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21
Combine remaining Parmesan and bread crumbs; sprinkle over top.
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22
Cover with foil, and refrigerate until ready to serve (up to 1 day); bring to room temperature before heating.
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23
Heat oil in a medium skillet over medium-high heat.
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24
Toss shallots with remaining 2 tablespoons flour.
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25
Fry shallots in 2 batches, turning frequently, until golden brown, about 3 minutes.
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26
Using a slotted spoon, transfer shallots to paper towels to drain; let cool completely.
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27
The shallots can be stored in an airtight container at room temperature up to 1 day.
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28
Preheat the broiler, with rack about 8 inches from heat.
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29
Cook casserole, covered, until mixture is bubbling and heated through, about 10 minutes.
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30
Uncover, and cook until top is golden brown, about 30 seconds.
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31
Remove from oven.
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32
Sprinkle with fried shallots.
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33
Serve immediately.
