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preheat the oven to 350 degrees.
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take the potatoes out of the freezer
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heat a large, deep cast iron skillet over medium-high heat, then melt 6 tablespoons of the butter in it.
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add the onions and cook, stirring occasionally, until the onions start to soften, 2 to 3 minutes.
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sprinkle the flour over the onions and stir to incorporate.
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cook for a minute or 2 to cook out the raw flour, but do not let it color.
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whisk in the milk, making sure to get out all the lumps.
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add the broth and whisk again if there are still lumps.
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bring the mixture to a simmer and allow it to thicken, about 3 minutes.
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season to taste with salt and pepper.
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turn off the heat and stir in the monterey jack, sour cream and cheddar.
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add the hash brown potatoes and mix everything together.
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melt the remaining 1 tablespoon butter in a small pan.
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put the potato chips and parmesan in a bag and crush the potato chips.
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pour in the melted butter and toss to coat.
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sprinkle the crumbs over the top of the potatoes.
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bake for 25 minutes