Prepare a baking sheet by lining it with parchment paper and set aside.  

In a medium-size heavy pot, combine the granulated sugar, brown sugar, salt, evaporated milk, and butter. Cook and stir with a wooden spoon over medium heat until the sugars dissolve and the mixture comes to a boil.

Continue to cook until the temperature reaches between 235-240 degrees F on a candy thermometer (soft ball stage). Remove from heat and allow the praline mixture to cool for 5 minutes.

Stir in the vanilla and pecans, beating by hand with a wooden spoon just until the candy begins to lose its glossiness and thickens slightly, about 2 minutes. If you beat too long, the candy will seize and start to crumble. If you don't beat it long enough, then pralines won't set properly and will stay soft and sticky.

Work quickly to drop heaping tablespoons (I use a small cookie dough scoop) of pecan praline mixture onto the parchment paper-lined baking sheet. If the praline mixture begins to harden in the pan, add a teaspoon of hot water at a time and stir to keep the mixture loose enough to scoop and drop. 

Cool completely until set and the pralines have reached room temperature. Store in an airtight container on the counter for 2 weeks or freeze for up to 2 months.