Instructions
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Melt butter and olive oil in a skillet over medium heat.
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Add onions and cook slowly, stirring often, until soft and deeply golden (15–20 minutes).
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Add garlic and cook 30 seconds until fragrant.
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Sprinkle flour over the onions and stir constantly for 1–2 minutes to cook out the raw flour.
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Gradually whisk in broth, scraping up any browned bits.
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Stir in cream and Worcestershire sauce.
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Simmer until thick, smooth, and glossy. Season with salt and pepper.
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Taste. Adjust. Guard the pan.