I have a question about the recipe "Madeira Tart" from thirschfeld. The recipe says, "...Pour the custard into the tart till it is half full. Place the tart into the oven and then finish filling the tart. You will probably have about a 1/2 cup of base left...." I am confused about why you would fill the tart half full, then place it in the oven and finish filling it. How could you fill it when it is actually in the oven? Thank you!