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1
If making ahead.
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2
Do not bake.
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3
Cover with plastic wrap, and refrigerate for up to 24 hours.
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4
To serve, remove plastic wrap and heat the casserole in a 350 oven for 30 minutes, then add the topping as directed.
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5
To serve, heat casserole in a 350 oven for 10 minutes uncovered, then add the topping.
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6
Bake until top is golden brown and sauce is bubbling around edges, about 5 minutes.
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7
For the Topping: Pulse bread, butter, salt, and pepper in food processor until mixture resembles coarse crumbs, about 10 1-second pulses.
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8
Transfer to a large bowl and toss with onions and set aside.
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9
Store in large zip-lock bag.
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10
For the Beans and Sauce:
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11
Fill large bowl with cold water.
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12
Bring 4 quarts of water to a boil in a large Dutch oven.
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13
Add 1 tsp salt and beans.
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14
Cook beans until bright green and crisp-tender, about 8 minutes.
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15
Drain beans in colander and plunge immediately into cold water to stop cooking.
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Spread beans on paper-towel lined baking sheet to drain.
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Add butter to now empty Dutch oven and melt over medium-high heat.
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18
Add garlic, 3/4 tsp salt and 1/8 tsp pepper.
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19
Saute 1 minute.
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20
Add flour and cook for 1 minute, stirring constantly with wire whisk.
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21
Stir in broth and bring to a simmer, stirring constantly.
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22
Add cream, reduce heat to medium, and simmer until sauce is thickened and reduced to 3 1/2 cups, about 12 minutes.
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23
Add green beans to sauce and stir until evenly coated.
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24
Arrange in an even layer in a 13x9 inch baking dish.
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25
Cover with plastic wrap.
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26
Refrigerate up to 24 hours.
