Grease a 12x15 inch sheet cake pan.

In a medium pot, combine the white and brown sugars, the corn syrup, butter, heavy cream, and evaporated milk. Cook the mixture over medium heat, stirring constantly. When a candy thermometer reaches 250 degrees F, remove the pot from the heat and stir in the vanilla.

Pour the caramel mixture into the prepared pan and let it cool almost completely (but still soft enough to cut) before cutting the caramel into small 1 inch long bars. Wrap each caramel bar in wax paper, twisting the ends.