Combine all ingredients in a blender and puree until smooth. Empty puree into a saucepot. Bring mixture to a simmer and simmer, stirring, until reduced by 1/2, approximately 20 minutes. You might see the butter separating, and that’s ok, just stir it back into the mix.
Empty mixture into a heat proof bowl and refrigerate at least 1 hour, or until completely cooled and thickened to a frosting consistency. If you want to speed the cooling process, place bowl on top of a bowl of ice and stir. It should chill in 5-10 minutes. Frost cupcakes with a piping bag or simply use a butter knife. Optional toppings might include slices bananas or strawberries, toasted coconut flakes, grated dark chocolate or crushed freeze-dried strawberries. Note—you might have some leftovers after frosting the 12 cupcakes. I like to dollop it over oatmeal or spread a thin (or thick!) layer on toast.
Cupcakes will keep tightly sealed in the refrigerator up to three days.