Melt the butter in a saucepan over medium heat. Add the walnuts, stirring constantly. Add the brown sugar and cook until melted. Remove from the heat and carefully add the bourbon. Return to the heat and cook out the alcohol, about 3 to 5 minutes. Be careful as mixture may ignite. Add cream and bring to a slow boil. Combine milk and cornstarch.
Add milk mixture into sauce stirring constantly until thickened.