Add the pancetta and butter to the casserole and cook over low heat until the pancetta is slightly crisp, about 4 minutes. Add the shallots and cook until softened but not browned, 3 to 5 minutes. Stir in the flour and cook, stirring, for 1 minute. Stir in the tomato paste and then the wine and simmer, stirring, for 3 minutes. Whisk in the stock until smooth and bring to a boil. Return the lamb to the casserole and simmer over low heat, skimming a few times, until the lamb is tender, about 1 hour. Drain the dried beans, add them to the stew and simmer for 15 minutes longer.