In a big bowl, mix together flour, salt, pepper and onion powder (if you use a fresh onion put it in with the liquid instead).
Dredge the ribs in the mixture and then assemble in an aluminum foil pan with a bit of oil. Broil in the oven until they are browned.
While you're browning - mix together all the other ingredients (fresh onion if applicable) using a wire whisk.
Peel and cube potatoes and arrange them in the bottom of the crock pot - season with salt.
When meat is browned, place on top of the potatoes and pour the liquid mixture over it.
Cook for 6 hours on high - or longer on low.
During the last 2 hours or so, mix it up.
During the last hour - mix it again and put in the mushrooms.
When the crock is done cooking - remove meat; remove potatoes. Use Flour - 1 tbsp at a time to make the gravy smooth and thick - depending on how much liquid you have you'll need to keep adding the flour until smooth (I use a wire whisk and do this directly in the crock pot).
Serve the potatoes and meat in separate plates with the gravy on the side.
As an aside, the gravy is really delicious so you could omit the potatoes from the crock pot and do mashed potatoes instead.
I do NOT use carrots because their taste contaminates everything in the crock pot and makes everything taste like carrots.
I do NOT use a fresh onion because the flavour is sometimes too overpowering.