I like to keep myself sharp by doing cornering drills in a parking lot or low traffic road. The key is consistency, not speed. What you need is the ability to believe that you can execute *exactly* what you plan to. Hit the brakes and trail them off at exactly the right time. Dive in with the right amount of aggression. Clip the apex exactly as you planned. Keep your head up, looking at the vanishing point the entire time.
Once you're able to do the exact same turn at the exact same speed holding the exact same line something like 10-20 times, the confidence will return automatically. From there it's just a matter of slowly and steadily pushing your limits.