Combine brown sugar, cream, corn syrup, and butter in a saucepan and stir over low heat until sugar is dissolved.
Set candy thermometer in place.
Cook to 238°F (soft-ball stage), stirring occasionally to avoid scorching.
Remove from heat; add extract without stirring; cool to 110 F.
Beat until thick and creamy.
If desired, add 1/2 cap chopped pecans.
Turn into a buttered pan.