It's actually mostly milk and sugar.
Here's the recipe:
3 medium sized eggs (or 4 smaller ones)
3 packages of vanilla sugar (each package is about 7 gram here)
150g of self-raising flour
Separate the egg yolk from the whites. Mix all the dry ingredients first and then add the wet ingredients to it except for the egg whites (for now).
Beat the egg whites to snow until you can hold the container upside down without them pouring out. Then stir it gently with the rest.
Butter your tin and sprinkle it with some self-raising flour. Make sure to pick a tin that won't leak! The batter is very liquid at this stage.
Add the batter to the tin and bake for 40 minutes at 200°C.
After baking, you can place the pie (gently) upside down on a roster to cool down. Make sure it's well baked before flipping it or you'll have a messy kitchen
The upside down is to make sure that some moisture still in the cake at the bottom will distribute to the top, making the whole cake moist again. The roster will leave it's figure in the top.
After cooling down, you can sprinkle it with some powdered sugar or add whipped cream.
It's not really hard to make but if you mess up you can easily get a messy kitchen at 3 stages:
1. If your egg whites aren't beaten enough and you hold them upside down to check
2. If your tin isn't leak proof your batter will just go everywhere. Maybe you can test it with water before hand? If water can stay in for at least an hour without leaking it should be okay I guess? I used a flexible pie tin instead of a metal one.
3. If your cake isn't baked long enough or warm enough and you didn't check before flipping your pie to cool (Check it by using a fork, if it comes out clean it should be okay, if it comes out wet bake it some more.)
2 out of those 3 has happened to me when I first tried to make this pie. Luckily it hasn't happened this time! (I've never messed up with the egg whites).