Line a baking sheet with parchment paper; set aside. Whisk sugar and sour cream in a 4-qt. saucepan until smooth; bring to a boil. Cook, stirring constantly, until mixture is bubbling and thick, about 5 minutes. Remove from heat; stir in pecan halves and vanilla extract until well coated. Spread on prepared baking sheet; let cool completely. Break into bite-size pieces before serving.