Hi – I’m wondering if your toffee was still a little too hot? For this to work, you want the toffee to be completely cool before dipping in the chocolate. Another potential problem is the quality of your white chocolate chips. Some chips have a coating that makes it difficult for them to coat and harden. I recommend using a high quality chocolate like ghirardelli, lindt, or cadbury. You can even try white chocolate candy melts and see if that helps! Good luck!