INGREDIENTS
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3 Tbsp. butter, plus more for greasing
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2 medium onions, chopped
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1/2 pound bacon (about 10 slices)
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2 cups all-purpose flour
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1 Tbsp. baking powder
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2 tsp. kosher salt
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1/2 tsp. ground black pepper
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1 cup whole milk
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1/3 cup extra-virgin olive oil
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1 egg
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1/2 pound Gruyère cheese, shredded (about 2 cups)