Gently boil the potatoes and garlic until tender. Meanwhile, heat the oil in a large skillet. Season the cutlets with salt and pepper; coat in the flour, shaking off the excess. Cook the cutlets until nicely browned, about 2 minutes per side. Drain the excess fat from the skillet, pour in the stock/flour mixture, add the sage, and bring to a simmer. Simmer 5 minutes, or until a sauce thickens around the pork. Reserve on low heat until the potatoes are done.
When cooked, drain the potatoes well and mash. Whip in the milk and butter; season with salt and pepper. Arrange the cutlets on plates with a scoop of the potatoes alongside.