Cookie dough: mix flour, sugar and baking powder. Rub the room temperature butter into the flour. Add the egg and combine just until you have an lump of dough. Refrigerate the dough for 1-2 hours.
See my guide on how to make the egg custard cream. Turn your oven on to 390°F/200°C. Cut the cookie dough in 0.2 inch pieces.
Roll the dough as thin as you can. Make them bite size. You can use this cookie dough as a basis for all kinds of cookies by adding ginger, chocolate chips, nuts or what ever you like
Transfer cookie to baking sheet, and place a teaspoon of egg custard at the middle of the cookie.
Make a similar piece of cookie dough and place it on top of the other one.
Don't worry too much about gaps, they will bake together in the oven. Bake in the middle of the oven for 15 minutes.
Cool down the cookies. Will keep in an airtight container for a week or so. I only used 1/3 of the cookie dough. The rest is in the fridge, waiting to be baked within the next month.
They are delicious.