For the cake:
400 g AP flour
120 g butter (although the original called for lard) at room temp
120 Powdered sugar
1 tsp baking powder
1 egg at room temp
approx 1/4 cup sour cream or whole milk
For the cream filling (ermine icing):
500 ml whole milk
5 Tbsp flour
2 Tbsp granulated sugar
200 g butter at room temp
200 g powdered sugar
2 Tbsp cocoa powder
For the glaze:
120 g powdered sugar
5 Tbsp cocoa powder
100 g butter
For the cake:
Equipment: 3 baking sheets and 6 sheets of parchment paper cut to fit baking sheets
Preheat oven to 350F. Combine dry ingredients in the bowl of a stand mixer fitted with the paddle attachment and mix briefly to combine. Add in butter and mix at medium low speed until it resembles coarse bread crumbs. Add in egg and mix again. Add just enough sour cream or milk slowly until the dough starts to come together.
Turn out onto a lightly floured surface and knead briefly until the dough is firm and homogenous in color. Separate into 3 equal pieces. Roll out each piece between two pieces of parchment paper until very thin. Each piece should be about 13x18" but it does not have to be perfect, the cake layers will be trimmed later. Remove the top parchment paper and slide onto a baking sheet. Bake each cake layer for about 15 minutes or until just starting to turn golden on top. Cool briefly and trim into equal sized rectangles then cool completely on a rack.
Make the cream filling:
Whisk milk, flour and granulated sugar in a medium saucepan over medium heat. Continue whisking until it comes to a boil, then remove from heat and allow it to cool completely.
Beat the butter and powdered sugar for 3-4 minutes or until light and fluffy. Add the cooled flour mixture slowly while the mixer is running and then turn up to medium speed. Beat until light and fluffy resembling whipped cream. If mixture becomes too runny it means that your butter has gotten too warm -- stick it in the freezer for 5-10 minutes then whip again until thick.
Add the cocoa powder to half the filling and mix well.
Assemble the cake:
On a serving dish layer the components in the following order: cake, chocolate cream filling, cake, white cream filling, cake. Chill while you make the glaze.
To make the glaze:
Combine all ingredients and 5-6 Tbsp of water in a small saucepan over low heat. Stir until the butter is melted and you have a thin sauce . Let cool to 90F.
Pour cooled glaze over entire cake. You can use an offset spatula to spread the glaze over the entire cake but it you will lose some of the shine. Chill the cake overnight or in the freezer until firm (about 1-2 hours). Trim the sides with a sharp knife and then cut into 2"x4" pieces. Can be stored in fridge for 1-2 days and served cold.