Attach a candy thermometer to a heavy bottom pot and add the sugar, brown sugar, and evaporated milk. Stir until it dissolved over medium heat with a wooden spoon.
Continue to stir until the mixture reaches 240° F. Remove the pot from the heat and drop the cubes of butter in without stirring. Let it sit for thirty seconds.
Sugar burns quickly. Keep an eye on it!
Add the vanilla and the pecans and stir with a wooden spoon. The candy will begin to thicken and become lighter in color.
Work quickly and spoon the mixture onto the prepared pan with a spoon.
Allow the Southern Pralines set for thirty minutes. When they harden they are ready to eat and share. They can be stored in an airtight container for up to three weeks.