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1
Adjust oven racks to middle positions and preheat oven to 400u00b0F. Toss cauliflower with 4 tablespoons olive oil and salt and pepper to taste. Divide between 2 rimmed baking sheets and roast, stirring occasionally, until deeply browned and tender, about 25 minutes. Remove from oven.
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2
Meanwhile, lay bacon slices in a cold cast-iron skillet, then set over medium heat. Cook, flipping once, until browned and crispy, about 6 minutes. Drain bacon on a paper towel, then chop or crumble into bite-sized pieces.
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3
Heat 2 tablespoons olive oil in a large, heavy-bottomed Dutch oven set over medium heat. Add onion and cook, stirring occasionally, until onions are translucent but not browned, about 6 minutes. Add roasted cauliflower and stock, bring to a boil, reduce heat, and simmer for 5 minutes.
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4
Let soup cool slightly, about 10 minutes. Add half and half and use a hand blender to blend soup until smooth. Alternatively, blend soup in a blender in two batches. Season to taste with more salt and pepper. Keep soup warm.
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5
Combine remaining 1/2 cup olive oil and parsley in blender and blend until smooth, about 1 minute. Pass oil through a fine-meshed sieve.
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6
To serve, ladle soup into bowls, garnish with parsley oil, and sprinkle with chopped bacon. Serve immediately.
