Melt butter in Dutch oven; use a brush and some of the melted butter to grease a heavy-duty foil-lined 9"x9" pan; set aside.
Add milk and next 4 ingredients to Dutch oven. Cook, stirring constantly, over medium high heat 35 to 38 minutes until mixture reaches firm-ball stage (250 degrees). Remove from heat and stir in vanilla. Quickly pour caramel into prepared pan. Let stand at room temperature or in the refrigerator until firm.
Lift out caramel and invert onto a cutting board; remove foil. Cut into 1"x1" squares; wrap each square with wax paper and twist ends.