This time when I made my lemon buttercream filling, I didn’t use any cream. I blended room temperature butter with the powdered sugar [a/k/a confectioners’ sugar or icing sugar]. I looked in the fridge and saw that the heavy whipping cream was a day away from expiring. Not wanting to take a chance, I decided to add the lemon curd. I added just the right amount to make it much tarter than in the past.