Pat the pork ribs dry with paper towels. Rub generously with salt and pepper. Toss with the flour until every inch is coated. Shake off any excess.
Heat the oil and half of the butter in a pan. Brown the pork ribs on all sides. Scoop out and set aside.
In the remaining oil, saute the celery, carrot, onion, garlic, rosemary and thyme until the vegetables are softened.
Pour in the beer and scrape to loosen any browned bits sticking to the bottom and sides of the pan. Let boil for a minute. Stir in a little salt and pepper.
Arrange the browned pork ribs in the pan in a single layer.
Cover the pan, lower the heat and simmer the pork ribs for an hour or until fork tender.
Scoop out the pork ribs and transfer to a plate.
Stir the cornstarch in two tablespoons of water. Pour half into the sauce and stir until the sauce is thickened and no longer cloudy. If the sauce is still too thin, pour in the rest of the cornstarch solution.
Add the remaning butter to the sauce. Stir until melted and incorporated. Taste the sauce one last time and add more salt and pepper, as needed.
To serve, arrange the pork ribs on a plate and spoon some of the sauce and vegetables over them. Optionally, sprinkle with snipped parsley.