In a large heavy saucepan, combine brown sugar, cream, corn syrup and salt. Bring to a boil over medium heat, stirring constantly. Cook until a candy thermometer reads 230° (thread stage), stirring occasionally.
Carefully stir in pecans and butter. Cook, stirring occasionally, until a candy thermometer reads 236° (soft-ball stage).
Remove from the heat; stir in vanilla. Beat with a wooden spoon until candy thickens and begins to lose its gloss, about 4-5 minutes.
Quickly drop by heaping tablespoonfuls onto waxed paper; spread to form 2-in. patties. Let stand until set. Store in an airtight container.
We recommend that you test your candy thermometer before each use by bringing water to a boil; the thermometer should read 212°. Adjust your recipe temperature up or down based on your test.