I made my normal buttercream tonight (1/3 c butter (room temperature), 1 c shortening, 3/4 c milk, a splash of vanilla, bag of powdered sugar). Made it like I always do - cream butter and shortening, add milk and vanilla then sugar. Beat it for about 15 minutes....same way I've been making it for the last 4 years However, when I went to use it on my cake, I noticed little lumps of butter that did not mix into the other ingredients. Is there any way to salvage this icing?
Take a lump out and check it. If it is ok, keep mixing. These lumps may have been just colder for some reason. Good luck.