Combine the sugar and milk and cook slowly in a heavy pot over a low flame until it reaches the soft ball stage (238 degrees on a candy thermometer). Remove from heat and add the butter, vanilla and pecans. Beat mixture with a wooden spoon until it is smooth and creamy. Drop by spoonsful onto waxed paper. If the candy does not harden within 10 minutes, it may be cooked some more.

I know the instructions say 238, but I always pull slightly before, closer to 235-236.