Combine pudding mix, sugar, milk, and butter in a large heavy sauce pan and stir until sugar begins to dissolve.
Cook over low heat, stirring constantly until sugar has dissolved. Then cook without stirring until the mixture reaches 238 degrees F on a candy thermometer (or until a small amount dropped in cold water will form a small ball.
Remove from heat at once, stir in pecans and beat with a spoon until mixture begins to thicken, about 2 or 3minutes.
Drop by tablespoon about 2 inches apart on a sheet of waxed paper. If mixture hardens as you work, set the pan over a pan of hot water, or add a drop or two of hot water and beat.
Let stand until firm, then store in an airtight container.