Grease an 8-inch square baking dish.
In a saucepan, combine the condensed milk and brown sugar. Cook over medium heat, stirring constantly, until the sugar has completely dissolved.
Add the butter and continue stirring until the mixture has thickened and the butter has melted.
Remove the saucepan from heat and stir in the vanilla extract and pecans.
Pour the mixture into the greased baking dish and spread it evenly. Allow it to cool for at least 2 hours.
Once cooled, cut the fudge into small bite-sized pieces.
Serve and enjoy!