Line your counter or two large baking sheets with sheets of wax paper.
In a heavy-bottomed saucepan, combine the brown sugar, granulated sugar, and evaporated milk over medium heat. Stir until the ingredients are well blended and the sugar dissolves, allowing the mixture to come to a boil.
Attach a candy thermometer to the side of the saucepan. Boil the mixture without stirring until the thermometer reaches 235°F (soft-ball stage).
Once the mixture reaches the correct temperature, remove the saucepan from the heat. Stir in the softened butter and vanilla extract.
Using a wooden spoon, beat the mixture rapidly for about 2–3 minutes, or until it begins to thicken and loses some of its glossy appearance.
Stir in the chopped pecans until evenly distributed throughout the candy mixture.
Quickly drop spoonfuls of the mixture onto the prepared wax paper.
Allow the candy pieces to cool completely and set before serving.
