• Place the sugar, honey, and butter in a saucepan. Stir gently until combined, then turn on low heat and melt the mixture, stirring constantly so it does not overheat. Once melted, remove from the heat and let it cool down.
• In a separate bowl, sift together the flour, cocoa powder, and baking soda through a fine sieve until the dry ingredients are evenly mixed.
• Gradually add the flour mixture to the cooled honey mixture, mixing and kneading until a dough forms.
• Beat the egg lightly with a fork, then add it to the dough. Make sure the dough is no longer warm, otherwise the egg can curdle. Mix until fully incorporated.
• Divide the dough into 6 equal portions. Using a rolling pin, roll each piece into a round sheet about 8–10 inches (20–25 cm) in diameter and about ¼ inch (5 mm) thick.
• Lightly dust a sheet of parchment paper with flour so the dough does not stick, place one rolled sheet on it, and bake each round at 375°F (190°C) on the middle rack for about 10 minutes. Let the cake layers cool completely, then trim the edges to obtain even, uniform circles.
• Whip the sour cream until slightly thickened, then gently fold in the sweetened condensed milk until you get a smooth, creamy filling.

Assemble the cake:

• Spread a generous layer of cream over the first cake layer, then sprinkle with chopped walnuts. Repeat this process 5 more times, stacking all the layers with cream and nuts.
• Place the remaining baked sheet and all trimmed edges into a blender or food processor and grind into fine crumbs. Coat the top and sides of the cake with the crumbs. Decorate with whole walnut halves and dust with powdered sugar. Refrigerate the cake for a few hours so the layers can soak up the cream before serving.