DO NOT DO WHAT I DID: I stopped after adding 3/4 or 1 cup powdered sugar. It seemed sweet enough to me at that point. Since I didn't have a sifter, I had little lumps of sugar in the filling--I would recommend sifting! I put it in the fridge for 2 hours while I worked on the cake. The taste of the filling before putting it in the fridge reminded me of licking the batter spoon as a kid--so that's what I did. Yum! When I took it out of the fridge it had a thick consistency and I spread it onto the first layer of cake and placed my second layer on top. This is when DISASTER struck. As I was icing the second layer, the filling began to reach room temperature again and melted back into liquid consistency! Soon I was battling to keep the top layer from sliding off the cake as the filling oozed out the sides. I put it into the fridge hoping to cool the filling back to a thick consistency. I still had to adjust the top layer every few minutes to keep it from sliding completely off until finally the filling cooled down. The taste was pretty good, but I guess unless you put all the sugar in, it won't get thick enough. So for me, this recipe would probably be too sweet--though it did seem to mellow a little in the fridge. Anyway, good luck, and don't do what I did!