Step 1

Heat oil in a large pot over medium heat. Add onion, leeks, celery, and garlic; season with salt and pepper and cook, stirring occasionally, until vegetables are soft, 10–12 minutes. Add potatoes and ham. Cook, stirring occasionally, until potatoes are just softened, 8–10 minutes. Add ham bone, thyme sprigs, bay leaves, and split peas and add water to cover. Bring to a boil, reduce heat, and simmer, uncovered, until peas are very soft and falling apart, 1½–2 hours.

Step 2

Remove ham bone (along with any meat that is still attached), thyme sprigs, and bay leaves from soup. Add Worcestershire sauce; season with salt and pepper.

Step 3

Serve soup with sour cream and croutons, if desired.