How to Make It
In a large heavy pot, heat the oil over medium heat until hot, then brown the pancetta, stirring occasionally, about 6 minutes.
Stir the onions, garlic, 3/4 teaspoon salt, and 1/2 teaspoon pepper and cook, stirring occasionally, until golden, 8 to 10 minutes. Peel and dice the potatoes. Stir in the potatoes, stock, tomatoes, Parmesan rind (if using), and oregano, and bring to a gentle boil. Cook the soup, stirring occasionally, until the potatoes are very soft and starting to fall apart, 45 minutes to 1 hour. Remove the Parmesan rind. Season the soup with salt and pepper to taste and serve.