1. Combine sugar and evaporated milk in large sauce pan. Bring to a tolling boil.
2. Keep at a rolling boil on medium heat for exactly 12 minutes, stirring almost continuously.
3. Remove from heat and add remaining ingredients. I slice the butter thinly before adding to sugar and milk mixture. Fold in and stir the chocolate chips and butter until well mixed.
4. Pour into Pyrex baking dish and let cool. Chill before serving.
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