I did a batch of basic butter cakes, with butter, sugar, eggs, flour, baking powder and milk. I mixed all the dry ingredients together beforehand and used a whisk to whisk them through before mixing them into the butter and egg mixture.
My cakes came out with little brown spots on the outside, and only the outside, not the inside. The cakes don't have any weird taste at all so it's just the aesthetic issues but it kinda bothers me since they look much less appetizing with those spots on them. I thought it maybe the baking powder since it was kinda old, but the brown sopts don't appear inside and they have no bitter taste so I'm a bit confused.
Any idea what can cause this? Thank you for the help.