Why does my lemon tart filling sometimes curdle? My recipe, which is wonderful when it goes well is:


grated zest and juice of 2 lemons
142 mL double cream
6 oz castor sugar
4 large eggs

Whisk all ingredients together, then pour into pastry shell and top with a lemon and gin glaze..

The mixture sometimes curdles at the whisking stage and looks like scrambled egg, and looks as though the mixture is &quot;cooking&quot; in the lemon juice.
Why does this happen and what can I do about it?
RockyFord's comment has the heart of the matter, I think--the acid in lemon juice will begin to denature or curdle to the proteins in the eggs if it comes into direct, undiluted contact with them.

You can minimize this effect by beating together all of the ingredients except the lemon juice prior to mixing in the lemon juice.  This will add a lot of sugar and milkfat which will buffer the interaction between the citric acid in the lemon juice with the egg proteins. 

You can then bake your tart as normal.