Magical Frosting, Cross Between Swiss Buttercream and Whipped Cream Frosting

INGREDIENTS

• 1/4 teaspoon Grated Lime Zest (it may be optional but I find that it somehow complements well with the vanilla and heightens the flavor of the frosting without necessarily turning it into a lime flavored frosting)
• 1 cup Granulated Sugar
• 6 tablespoons All Purpose Flour
• 1 1/2 teaspoon Pure Vanilla Extract
• 2 tablespoons rum
• 2 Sticks (1 cup) Unsalted Butter
• 1 cup Whole Milk