Reduce the heat in the oven to 160°C or 300°F.
Grate the 4 lemons and squeeze them. Once you have squeezed the juice from them strain it and add it to the grated rind.
In a bowl large enough to hold all the wet ingredients break the eggs, add the plain sugar and beat lightly to dissolve the sugar. You don’t really want to beat any air into the mixture you just want to dissolve the sugar.
When done add the lemon rind and strained juice and mix in well then add the cream and mix again.
Pour half the liquid into the waiting tart shell and place it on a baking tray in the middle of the preheated oven. Pour in the rest of the egg mixture into a water pitcher. Pull the oven rack half way out and pour in as much of the filling as you can.
Using a pitcher like this means that you don’t have to balance a tart shell full of cream across your kitchen dripping all over the floor.
If you are using the 22cm. quiche pan you should have a little filling left over - don't throw it a way. Grease a small oven proof dish just large enough to hold the extra liquid and bake for about 20 minutes after the tart comes out of the oven. It will be a little extra treat.
Very gently slide the oven rack and tart into the oven. Using the traditional tart pan of 27cm. (11in.) bake at 160°C or 300°F for about 60 minutes or just until the filling sets. Using the 22cm. (8-1/2in) quiche tin bake at 160°C or 300°F for about 1hr. 30minutes, or just until the filling sets.
Remove from the oven and let cool. Take a paring knife (very sharp knife) trim off the extra short pastry using an outward cutting motion trimming all the extra pastry taking care not to touch the top of the lemon filling. Take the remaining powdered sugar and place it in a fine strainer and sprinkle it over the top of the lemon tart to decorate it.