It was the Big Uh-Oh. An inch of lemon poppy seed sludge was left in the bottom of the KitchenAid mixer bowl when I poured out my cake batter. Could the gap between the bottom of the paddle and the bottom of the bowl be out of adjustment?
It was easy to find out and all it took was one thin dime.
It's called the "dime test." Place a dime in the bottom of your steel KitchenAid mixer bowl and attach the paddle. Raise the bowl to its working position, or if you have a tilt head model just tilt the head down. Turn the mixer on at speed 1. If the paddle pushes the dime along all around the bottom of the bowl, there's not enough clearance. If it doesn't move the dime at all there's too much.
But if the beater moves the dime just a quarter to a half inch on each revolution it's jusssssst right. If one of the first two you can lower or raise the beater using the adjustment screw in the neck of the mixer.
My mixer didn't move the dime at all. So I turned the adjustment screw. And it still didn't move the dime at all. So I turned it all the way. Still no joy. The bowl needed to come up a tiny fraction of an inch more, but there was no adjustment left. Now what? My brilliant solution is pictured below.
Just one washer on each of the mounting pegs shimmed up the bowl enough to get a perfect dime test.
IMPORTANT
1. This method only works with the KitchenAid steel bowl, not the glass or ceramic models.
2. Use the paddle attachment only, not the whisk or hook, for this test.
3. Turn the adjustment screw in the neck of the mixer only. Don't mess with any other screws.
Naturally, I called Nancy Leson immediately to tell her what a genius I was. Nance diplomatically reserved comment on that, but immediately set to testing her standing army of stand mixers.

I was so pleased with my hack that I immediately mixed up a batch of that Rosemary Shortbread we talked about a few episodes back. Hope I remembered to take that dime out first.
"A nickel ain't worth a dime anymore." –Yogi Berra