In a small bowl, combine flour and baking powder, set aside.
Separate the four egg yolks and whites into two separate bowls.
Add the sour cream to the egg yolks and beat with a mixer at high speed for 2 minutes.
Beat egg whites on high speed until whites go from soft/glossy and start to stiffen (about 3 minutes). Continue beating and slowly add the 2/3 cup sugar, beat until well incorporated.
Pour the egg yolk mixture into the egg whites and carefully mix with a spatula. Just until everything is combined, careful not to overmix.
Gently fold in the flour, mixing from the bottom up. Divide this mixture between two bowls. Add the poppy seed into one bowl and the cocoa powder into the second.
Pour the mixtures into the prepared pans.
Bake in preheated oven 12-15 minutes, check the center or cake for readiness with a toothpick.
Beat egg whites on high speed until whites go from soft/glossy and start to stiffen. Slowly add the 3/4 cup sugar, keep beating until stiff peaks form. With a spatula, fold in the chopped nuts.
Divide the mixture into the pans, evening out the top of layers as much as possible.
Bake meringues for 1 hour. DO NOT OPEN OVEN during baking. Turn off the oven and open the door halfway allowing the meringue to cool.
Turn the mixer to low and add the condensed milk, mix just until incorporated. Refrigerate cream until needed.
decor-
Blend vanilla wafers, walnuts and graham cracker. Combine everything for the decor to create a crumbly mixture.
assembly-
Once all of the layers are completely cooled, place the chocolate layer on your platter as the base. Add a generous portion of cream. Take 1 meringue layer, flip it over, remove parchment paper and place atop the chocolate layer. Add a thin layer of cream.
Take the second meringue and flip it over, remove parchment paper and place it over the first meringue. Add a generous portion of cream. Flip over the poppy seed layer and place over top of the meringues. Cover the sides and the top of the cake with the remaining cream.
decorating-
Take the décor mixture. Cover sides of the cake with it and around the rim of the cake.
Melt the chocolate and decorate create a design in the center.
Take a knife and starting at the top of the chocolate circle start pulling the knife vertically until you get to the bottom of the circle. The chocolate will pull as well and it will create a design. Next, take the knife and a small distance from where you just ended take the knife and go up. Do the same on the opposite side of the center, repeat until you reach the end of the circle.