Line a baking sheet with parchment paper.
In a heavy saucepan over medium heat, combine granulated sugar, brown sugar, butter, and cream. Stir until the mixture reaches 235°F (soft-ball stage) using a candy thermometer.
Remove from heat and stir in pecans and vanilla. Stir vigorously until the mixture thickens slightly.
Quickly drop spoonfuls onto the prepared baking sheet.
Let cool completely before serving or storing in an airtight container.