If the blade broke below the end of the stock, then clean it all up, feather back the skin on the remaining rudder. Try to find a similar core material and fashion a new piece to match the original, undersized by the skin thickness you plan to relaminate. Maybe leave room for thicker glass layers at the joint.
Then I'd put some pins into the original part of the blade, with matching recesses/holes in the new section, slide it together and glass it all up. Then refair the repair and seal and paint it. Using epoxy resins will likely work best, but vinylester may work too. There should be plenty of on-line help as the the specifics of the materials you should use.
If your rudder stock is undamaged, there's no need to worry about the rest of the rudder unless there's some play between the original blade and the stock.. that would indicate that you've possibly damaged the internal framework or the internal coring of the original part. There is a chance, though, that if you hit something hard enough to break a chunk clean off that you have in fact done more damage elsewhere that you simply can't see....
If you're lucky Jeff H will weigh in with more specific suggestions.... (and likely a better plan