How do I replace a JSON string with its parsed equivalent in place with jq?

I have a JSON array with a bunch of objects, all the same keys, but some of the keys contain serialized JSON instead of actual JSON. Something like this.

[  {"a": 1,"b": "{\"c\":2}"  },]

and I'd like to replace the contents of all the bs with their parsed form.

[  {"a": 1,"b": { "c": 2 }  },]

How can I do this, ideally with jq?