In a small saucepan warm up the milk, sprinkle yeast over it and let sit for 3-4 minutes. Stir and dissolve the yeast.
Mix in egg yolks and vanilla extract, set aside.
In a medium size bowl mix together flour, sugar and salt.
Add and toss the cut butter cubes until fully coated. Use a pastry blender to cut in the butter until mixture reassembles a coarse meal.
Add yeast mixture to the bowl and mix with wooden spoon until the flour hydrated. Use your hands to quickly gather together a shaggy mass until it holds together.
Knead on a lightly dusted counter for 2-3 minutes until you obtain a stiff and sticky dough.
Wrap the dough in plastic wrap and refrigerate for 1 hour.
Filling
In a food processor, process together walnuts and sugar until very fine texture is obtained.
Assembly and Baking
Butter and flour a 13″ x 9″ baking pan, tap out excess flour.
Warm up apricot preserves in a small saucepan.
Weigh and divide the dough into 3 equal portions. Roll out the first portion into a 13″ x 9″ rectangular shape. Meanwhile keep other two portions wrapped in the refrigerator.
Note: I prefer to roll the dough out on top of the plastic film. This makes it easier to handle (transfer, spread out etc.).
Transfer the dough to the baking pan, leave plastic film at the top. Gently fit the dough to the pan, press and fill the corners. Peel the plastic film off.
Spread and brush evenly 1/2 of apricot preserves on top of the dough.
Sprinkle with 1/2 of walnut mixture.
Roll out second dough portion into a 13″ x 9″ rectangular shape and gently fit in the baking pan following the same procedure as for the first dough layer.
Spread and brush evenly the reminder of apricot preserves, sprinkle on top with the reminder of walnut mixture.
Roll out a third dough layer into a 13″ x 9″ rectangular shape and gently fit in the baking pan following the same procedure.
Cover with plastic wrap and keep in warm place for 1 hour. At the same time prewarm the oven to 177ºC (350ºF), rack in the middle.
Use a fork and pierce all over the top dough layer.
Bake for 30-35 minutes or until the top is golden brown.
Let baking pan cool off for 15 minutes on a wire rack.
Run a knife around the edge of the pan. Invert the baking pan and unmold the cake on a wire rack. let cool completely.
Chocolate Icing
Over double boiler melt the chocolate, making sure the chocolate temperature does not rise above 50ºC (122ºF).
In a small sauce pan stir together sugar and water. Over medium heat bring to boil, stir continuously. Maintain the boil until instant read thermometer reads 104ºC(220ºF).
Remove from heat, add the chocolate to the sugar mixture, stir until smooth. Stir in the butter until melts and incorporates. Let the icing cool for a few minutes until it thickens up slightly. The icing should be lukewarm but still pourable.
Place the wire rack over the larger baking pan.
Pour the icing on top of the cake, spread evenly using an offset metal spatula.
Let the icing set overnight at room temperature.
Using a sharp knife that is dipped and prewarmed in hot water cut the cake in 12 squares. Serve at room temperature.
Cover with plastic wrap and store at room temperature.