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1
Pick 1/2 cup cilantro leaves and set aside. Combine broth, remaining cilantro stems and leaves, and Worcestershire sauce in a large saucepan and bring to a boil. Season to taste with salt and more Worcestershire sauce. Reduce heat to lowest setting, cover, and keep warm.
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2
Heat olive oil over medium heat in a small saucepan. Add onion and cook, stirring, until softened but not browned, about 5 minutes. Add tomato, cover with water, bring to a simmer and cook, stirring occasionally, until completely soft and reduced to a thick puree, about 10 minutes. Season to taste with salt. Transfer to a wide, shallow bowl and place in refrigerator.
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3
Rinse sliced potatoes under cold running water until liquid runs clear. Transfer to a kitchen towel or paper towels and dry thoroughly. Heat vegetable oil in a medium saucepan over high heat until shimmering. Add half of potato sticks and cook, stirring, until crisp but not darkly browned, about 5 minutes. Transfer to a paper towel-lined bowl with a wire mesh spider and season with salt. Repeat with second batch of potatoes.
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4
Combine bread, egg, and heavy cream in the bowl of a food processor. Process until a smooth paste is formed, about 30 seconds. Add beef, capers, and a 1 1/2 teaspoons of kosher salt and process until completely smooth and homogenous, about 2 minutes. Add onion and tomato mixture and process until smooth, about 30 seconds longer. With wet hands, form mixture into 3/4-inch balls (you should have about 24 balls).
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5
Remove cilantro from pot of stock and discard. Add meatballs and cook until they float and a meatball cut in half is no longer pink in the center, about 4 minutes. Use a slotted spoon or wire mesh spider to transfer meatballs to a bowl. Skim fat from top of soup and pour soup through a fine mesh strainer into a clean pot. Serve immediately, dividing meatballs between warmed serving bowls, ladling soup on top, topping with fried potatoes and remaining picked cilantro leaves.
