Pour milk, water, cream, and sugar into a large, heavy bottomed saucepan. Add the butter, and bring to a boil over medium-high heat, stirring constantly.
Step 3
Reduce heat to medium, and cook for 20 minutes, stirring constantly. After 20 minutes, remove from heat, and beat in vanilla extract. Continue to stir until the mixture is no longer glossy. Pour into prepared pan, and let cool until hard, about 6 hours.
