I make christina toosi/Milk Bar's chocolate malt cake (this version: http://milkbarstore.com/main/menu/rec...). This version of the recipe was, tbh, very poorly written (for examption, should probably be 20 g, not 60g of ovaltine in the crumb) but I figured most things out.
What really irritated me is that I got the butter to room temp, creamed it with the sugar, then then added the eggs. It looked fine so I added the buttermilk slowly and immediately the batter curdled so much it was just sickening. I researched batters curdling and everyone seemed to say it was the eggs that caused it, so I I figured I must have forgetton or missed something the first time around and decided to try again and let the eggs and butter get to room temp before adding. I was super careful about thoroughly creaming sugar and butter (still don't think I did that right tbh but have no experience to see what's right) and then added the room temp eggs and it was fine. Then I waited a bit before adding the buttermilk super slowly and it immediately starting curdling. It was awful but I just kept adding the rest of the ingredients and the batter eventually smoothed out. The recipe says the cake will be dense so I don't know if the final result was the density it was supposed to be or the curdling and perhaps over whipping hurt something. It turned out fine as far as I could tell but I wish I knew what happened.