In a large cast-iron pot, melt 1 tablespoon of the butter in 1 tablespoon of the oil. Season the pork with salt and pepper.
Add one-third of the pork to the pot and cook over moderately high heat, stirring occasionally, until well browned, about 8 minutes. Transfer the pork to a baking sheet. Repeat in 2 more batches with the remaining butter, oil and pork.
Add the bacon to the pot and cook until desired doneness; then add to the pork. Add the onion and garlic to the pot. Cook over moderate heat, stirring, until golden and softened, about 5 minutes.
Add the pork and bacon back to the pot along with the cider, stock and bay leaves; bring to a simmer. Cover and simmer gently until the pork is tender, 2½ hours. Discard the bay leaves.
In a small bowl, whisk the cornstarch with 1/4 cup of water. Add the cornstarch mixture and the cream to the stew and simmer until the liquid is thickened, about 5 minutes.
Stir in the mustard and sage and season with salt and pepper. Enjoy.