In a large saucepan, cook the pancetta in the oil over moderately high heat until browned, about 6 minutes. Add the dried cranberries and shallot and cook, stirring, until the shallot just starts to brown, 4 minutes. Stir in the spinach in large handfuls, letting each batch wilt slightly before adding more. Cook, tossing, until all of the spinach is wilted, 3 to 5 minutes. Season with salt and pepper, transfer to a bowl and serve.