1. Line a baking sheet with parchment. Melt butter in a saucepan over low heat. Stir in granulated and brown sugars, salt, and sour cream. Raise heat to medium-low, and cook, whisking frequently, until sugar has dissolved. Raise heat to medium-high. Cook, stirring frequently and scraping sides of pan with a spatula, until mixture reaches the soft-ball stage (240 degrees), 10 to 15 minutes.

2. Remove from heat. Carefully stir in bourbon and vanilla (mixture will steam and bubble). Let cool, without stirring, for 2 minutes. Add pecans, and beat vigorously with a spoon until slightly opaque but still creamy, about 2 minutes.

3. Drop spoonfuls onto baking sheet. (If mixture in pan begins to harden, stir in 1 teaspoon hot water, as often as needed; if it becomes runny, stir until firm.) Let stand until set, about 30 minutes.