First crumble the shortbread biscuits and knead with the butter and milk to form a dough. Press into a springform pan (26cm) and bake at 175 degrees (convection) for 15 minutes.
The lime juice (please leave 1 tablespoon, it will be used later), 3 egg yolks and the sweetened condensed milk (and here please only use the sweetened condensed milk, no other !!!! It works neither with normal condensed milk nor with sour cream or cream) Whip until creamy and pour onto the baked cake batter.
Beat the egg white together with the sugar and the rest of the lime juice until stiff and spread on the cake. Make little tips with a spoon! Bake at 150 degrees (convection) for 15 minutes, then switch off the oven and leave in the oven for another 5 minutes.
Serve lukewarm! Tastes great with coffee or sparkling wine.