Temperature needed to make crunchy toffee
Toffee is a confection made by caramelizing sugar or molasses
  (creating inverted sugar) along with butter, and occasionally flour.
  The mixture is heated until its temperature reaches the hard crack
  stage of 149 to 154 °C (300 to 310 °F). While being prepared, toffee
  is sometimes mixed with nuts or raisins.


As stated here - https://www.google.co.uk/webhp?sourceid=chrome-instant&amp;ion=1&amp;espv=2&amp;ie=UTF-8#q=toffee+temperature

Hope that helps...