Typically I leave my buttercream-frosted cakes out of the refrigerator. However, tonight I tried a new recipe that called for adding 1 tbsp lemon juice and 2 tbsp buttermilk (in addition to 1 cup butter and ~4 cups powdered sugar). Does the inclusion of cultured buttermilk warrant a night in the fridge, or is it safe on the counter? I plan on serving these in about 10 hours.
FYI: the result is a frosting that tastes like cream cheese frosting, but with a far creamier texture!