Bean and Ham Hock Soup with Kale and Croutons

Stock: In large stockpot or slow cooker, combine ham hock, onion, celery, thyme, bay leaves, peppercorns and 12 cups (3 L) cold water. Cover and cook on low heat, skimming off foam as necessary, for 4 hours on stove top or for 8 to 10 hours in slow cooker. Remove hock and let cool enough to handle. Discard skin, fat and bone. Using fork or fingers, shred ham. (Make-ahead: Cover and refrigerate for up to 2 days.) Strain stock through fine sieve into large bowl, pressing vegetables to extract liquid. Remove fat. (Make-ahead: Let cool for 30 minutes; cover and refrigerate for up to 3 days.) Croutons: In bowl, toss together bread, oil, salt and pepper; spread on rimmed baking sheet. Bake in 400°F (200°C) oven, tossing once, until golden and crisp, 6 to 8 minutes. Let cool on rack. (Make-ahead: Let cool; store in airtight container for up to 24 hours.) In Dutch oven or stockpot, heat oil over medium heat; fry onion, celery, carrots and garlic until softened, 8 minutes. Add tomato paste and pepper; cook, stirring, for 2 minutes. Add stock, cooked beans and shredded ham; bring to boil. Reduce heat and simmer, uncovered, for 20 minutes. Add kale; simmer until tender, about 7 minutes. (Make-ahead: Let cool for 30 minutes; refrigerate in airtight container for up to 3 days.) Serve topped with croutons.