
After looking at some recipe attempts on the internets and rejecting them as pretty gross-sounding (many were based on carbonated drinks, and one actually included melting vanilla ice cream and adding it to the soda), I found a recipe in a book which I was able to adapt. Not only is it delicious, but it has the advantage of including butter as its base. So I should note that, while it does not consist of melted ice cream, it is not exactly a health shake. But for an occasional indulgence, it's been well received around here.
Butterbeer
2 cups water
1/2 stick butter
1 packed cup brown sugar
1/4 cup sugar
pinch of salt
1 tsp cinnamon
1/2 tsp nutmeg
shake of ground cloves
1 cup heavy cream
1 cup milk
Melt the sugars and the butter in the water over high heat, whisking to dissolve the sugars in the liquid. After they are fully integrated, reduce the heat to low and add the salt and spices, heating until quite hot. Meanwhile, mix the cream and milk in a blender and process until frothy. (The dairy seems to thicken best if blended cold.)
Ladle 1/4 cup of the cream mixture into a mug, followed by 3/4 cup of the spice liquid. Stirring with the tip of your wand may be considered bad manners, but no one objects to seeing frothy mustaches from a hearty gulp of butterbeer.