We use some butter to grease a medium sized pan (preferably pyrex). We spread the pastry sheet and using a fork, we pierce the sheet throughout its surface. We put some baking paper over the pastry sheet, and then we place a metallic small pot or skillet on top, to press down the pastry while we bake it. We put the pan (with the pot) in the oven (middle rack) and bake for 10-12 minutes at 180 degrees Celsius. After we remove from the oven, we remove the paper and the pot and let the pastry sheet in the pan to cool down.
We whisk the eggs and the sugar in a large bowl. When the mixture becomes fluffy we add the cream, then the milk, the zest and finally the lemon juice. We whisk until the mixture is smooth.
We pour the mixture in the pan with the pastry, and put it in the oven (middle rack) at 180 degrees Celsius for 10 minutes. We sprinkle with the sugar we kept for frosting, and put it back in the oven for another 20-25 minutes.
We remove from the oven and let it cool down to room temperature before slicing and serving.
We serve with a cup of coffee or tea.