Place the chopped sweetpotatoes in a large pot and cover with salted water. Bring to a boil and cook for 15–20 minutes, or until fork-tender. Drain well and allow the sweetpotatoes to steam-dry for 2 minutes.
Add the butter, milk, salt and pepper. Mash until smooth and creamy, adding another splash of milk if needed. Divide the mash among four oven-safe bowls.
While the sweetpotatoes cook, heat the olive oil in a large skillet over medium heat. Add the ground beef and onion. Cook for 6–8 minutes, breaking the beef apart with a wooden spoon, until the beef is browned and the onion is tender. Drain any excess grease.
Add the garlic, paprika, cumin, oregano and chili powder. Cook for 30 seconds, stirring continuously, until fragrant.
Stir in the tomato paste and cook for 1 minute. Add the tomato puree, black beans, salt and pepper. Bring to a gentle simmer and cook uncovered for 10–12 minutes, stirring occasionally, until the chili has thickened.
Spoon the chili over the sweetpotato mash and sprinkle each bowl with shredded cheese.
Top with sour cream and fresh cilantro. Serve warm.