I bought my first All-Clad pan a few weeks ago and after it got a bit gunky from cooking, I dusted on some Barkeeper's Friend with some water and let it sit. (I know this wasn't exactly as per the instructions.) When I tried to wash it off, a white residue would not come off! I tried scrubbing it and even boiling some water in the pan, but nothing is working. I'm attaching a photo. What did I do!?