1. Line 2 baking sheets with parchment paper. (If using paper baking cups, place 16 cups on baking sheet or on a tray.)
2. Stir together sugars, buttermilk, cream, corn syrup, and salt in a heavy, 2-quart saucepan; attach a candy thermometer to side of pan. Place pan over low; cook, stirring constantly, until sugars are melted and mixture is smooth, 5 to 8 minutes.
3. Increase heat to medium-high, and bring mixture to a boil. Boil gently until the thermometer reaches 230˚F to 235˚F (soft-ball stage), 10 to 12 minutes. Remove from heat; let cool to 220°F, 6 to 8 minutes.
4. Using a wooden spoon, vigorously stir in butter and vanilla, stirring until mixture turns creamy and opaque. Stir in pecans and bourbon, and quickly spoon out 1⁄4-cup portions onto prepared baking sheets or into paper baking cups.
5. Let pralines stand until completely cool, about 1 hour. Serve immediately, or wrap each praline individually in wax paper or plastic wrap, and store in an airtight container for up to 1 week.