Holiday Baking : A dessert named "Lonci"

We first tasted this "cake" at my sister-in-law, and my husband loves it. So, he asked for the recipe from his sister. Nobody knows why the name "Lonci". We tried searching online with no result. For me, the looks is exactly like a Gerbeau slice, except for the fillings, of course.  I would say that the filling is too mild and the chocolate taste takes over. However, I do like the result of the pastry and this method of making butter cream intrigues me. Perhaps I'll test out the pastry and buttercream separately in other bakes in the future.

Lonci (Creamy Gerbeau Slice)

Ingredients

For pastry

400gm flour

1/2 sachet baking powder

120gm shortening (used goose fat)

120gm sugar (reduced to taste)

1 egg

sour cream , as needed (less than a cup)

For filling

200gm butter, softened

250gm powdered sugar (reduced according to my taste)

500ml milk

2 Tbsp sugar

4 heap Tbsp flour

flavourings :-

Rum

cocoa

1 tsp vanilla extract or 1 sachet vanilla sugarFor cocoa glazing

4 Tbsp water

8 Tbsp sugar

3 Tbsp cocoa powder

120gm butter

Method

For Pastry

1. Mix together all ingredients in a bowl except for sour cream. Add sour cream gradually and knead until you have a smooth dough
2. Divide dough into 3. Roll each dough out into a rectagular sheet and blind bake each sheet until golden brown in a meadium heat oven
3. 
   

For filling

1. Cream butter and sugar until light and fluffy set aside.
2. Cook milk, sugar and flour in sauce pan until it thickens. Place the thicken mixture onto cold water to cool. Stir the mixture continuously until cooled.
3. Mix together buttercream (1) and milk mixture (2) . Divide this into 2 portions.
4. One portion flavour with cocoa and rum ; while another portion add in vanilla extract or a sachet of vanilla sugar

For cocoa glazing

1. Bring water and sugar into a boil and mix in cocoa powder. Remove from heat and add in butter and mix until well combine

Assembly

1. Place 1 sheet of baked pastry onto serving dish, spread with all of cocoa flavour filling. Then place seconc sheet of baked pastry over it. Next spread vanilla flavoured filling over the pastry and place final baked pastry sheet on top.
2. Finish off by pouring cocoa glazing while glazing is still warm . Let cake rest for at least a day before serving.