The blobs in the batter are pieces of butter. This butter breaks out of the batter when the fat gets too cold and seizes. It's important that all fat and dairy, including butter and eggs, should be brought to room temperature before you use them in batter.

What do I do if my cake batter is lumpy?

How to Fix Curdled Cake Batter. One way to fix broken cake batter is to add a bit of flour, one tablespoon at a time, until it smooths out again. The flour helps the liquid and fat come back together and creates a smooth, lump-free mixture.

Is it OK to have lumps in cake batter?

It's possible that the little lumps is flour. That will happen sometimes if you don't sift the flour. But all is not lost...just put the batter through a fine sieve or strainer and stir the batter and scrape the bottom as it goes through. That should get rid of the little lumps.