Melt In Your Mouth Toffee

In a heavy saucepan, combine butter, white sugar, and brown sugar. Cook over medium heat, stirring constantly until mixture boils. Boil to brittle stage, 300 degrees F (150 degrees C) without stirring. Remove from heat.
Pour nuts and chocolate chips into a 9x13 inch dish. Pour hot mixture over the nuts and chocolate. Let the mixture cool and break it into pieces before serving.