[lashbear]

Yes, I can conofirm that for souffle(e?)s, merangues, sponges, Pavs and any other recipe requiring stiffly beaten egg whites that hold their volume, Cream of Tartar will make it hold until the cows come home.

Just a pinch, mind, you only need a little to make the magic work.

We often use it in deep frying batter too: make the egg-yolk, flour and water batter, whip the eggwhites with the cream of tartar, fold it through the batter, and you have puffy yummy batter that we use mostly for sweet and sour chicken.

...and I can believe that this recipe might work, because vinegar pie definately tastes of citrus / apples to me. (I use apple cider vinegar to make it, of course...) Therefore why not an apple pie of lemons.