Pie for a rainy afternoon

A very traditional Portuguese pie. It has different names but in my family we call it "Tarte Maria".
Warning: extremely rich, not advisable for the weak! 

250g (1 pack) of Marie cookies

170g of butter (no salt)

1 yoghurt (simple)

1 can of condensed milk

5 egg yolks and 3 egg whites
3 spoons of sugar

1 lemon 

Mix the cookies and the butter to make the dough for the base of the pie and cover the bottom of a pie pan with it.

Mix the condensed milk, the yoghurt and the egg yolks. Squeeze half a lemon´s juice (or more depending on personal taste) into that cream and mix a bit more. 

Pour the cream into the pie pan.

Beat the 3 egg whites until they are really hard and then add the sugar. Reserve this part and put the pie in the oven (pre-heated) at 180.C for 20min. 
Take out the pie and cover it with the beaten egg whites, then put it back in the oven until the top gets golden.
Let it cool down completly before eating.

Personal touch: after it cools down, and instead of using the beaten egg whites (remember to leave the pie in the oven for 30 min. then), you can sprinkle the top of the pie with cinnamon, crystallized ginger, chocolate, lemon or orange zest, almond in powder, or even some freshly picked herbs like basil or mint...take your pick. I am going to have mine with fresh strawberries (it helps to balance the richness of the pie) and little pieces of dark chocolate...

Bom apetite!