"This is called Italian Buttercream. I'm a pastry chef and use this recipe ALL the time. For any of you that had difficulty with this recipe not coming together, try using cold-tempered butter. What that means is don't leave the butter out until it is completely soft. Take the butter out of the refrigerator and allow it to sit for about 30 minutes. Cut it into 1tbsp portions. If you have a disposable glove now is the time to use it! (You could use a ziploc bag). When your meringue is at room temperature, take a piece of the butter and squish it in your hand then add it to the mixture. Let that piece incorporate, then add the next piece. If you add the butter slowly and let each piece incorporate and make sure that the butter is cool to the touch, it will come together. Buttercream is the most fixable thing so don't throw it out! Chill it down then whip the heck out of it on your mixer. If it's too cold, then take a hot towel and warm the sides of your mixing bowl while it mixes.