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1
In a large heavy skillet (I use my large cast iron pan or Le Creuset) over medium heat, cook the bacon and onion,stirring often, until bacon is lightly browned and the onion is softened (about 15 to 20 minutes).
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2
In a large measuring cup, stir the flour into the reserved liquid (or 1 1/2 cups water), whisking briskly with a fork until smooth.
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3
Pour the flour mixture all at once into the bacon and onion mixture; use a wire whisk and whisk briskly to combine. Use a wooden spoon to gently scrape browned bits from bottom of pan and incorporate them into the sauce.
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4
Cook and stir constantly (I use a wire whisk or wooden spoon) over medium-high heat until mixture comes to a boil. When mixture comes to a boil, continue to cook and stir on medium-high heat for 3 minutes more (at this stage you may want to add a touch more of water or flour, depending on how thick you want the sauce to be).
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5
Add the green beans, lemon zest, salt and pepper, and the fresh parsley (except one tablespoon snipped parsley, for garnish); stir to combine. Reduce heat to medium, stir occasionally until beans are hot (8 to 10 minutes).
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6
Remove from heat. Finish with a squeeze of fresh lemon juice and garnish with snipped parsley. Serve immediately.
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7
If making beans ahead, to serve later:
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8
At this point, spoon hot bean mixture into a 1 1/2 to 2-quart size casserole dish; let cool slightly then cover and refrigerate. About 1 hour prior to serving, remove from fridge and let sit at room temp for 15 to 30 minutes. Place the covered casserole into a preheated 350 degree F oven for 30 to 40 minutes, until hot. Garnish with snipped parsley and serve hot.
