Step 1: In a heatproof bowl set over a saucepan of simmering water (a double boiler), combine the butter, honey, and sugar. Stir occasionally until the butter is melted and the sugar has dissolved completely. The mixture should be smooth and slightly warmed. Do not let it boil.
Step 2: Remove the bowl from the heat. Whisk in the baking soda. The mixture will foam up considerably and lighten in color. Stir for about 30 seconds.
Step 3: Gradually add the beaten eggs to the honey mixture, whisking constantly to prevent the eggs from scrambling. If the mixture is too hot, let it cool for a minute before adding the eggs.
Step 4: Return the bowl to the double boiler. Gradually add 2 cups of the flour, whisking until smooth and lump-free. Cook for about 5-7 minutes, stirring continuously, until the mixture thickens slightly and develops a caramel-like color and aroma.
Step 5: Remove from heat and transfer the mixture to a large mixing bowl. Add the remaining flour, about half a cup at a time, mixing with a wooden spoon or a stand mixer with a dough hook until a soft, slightly sticky dough forms. Cover the dough and let it rest at room temperature for at least 30 minutes, or chill it for an hour.
Step 6: Preheat your oven to 350°F (175°C). Line several baking sheets with parchment paper. Divide the dough into 8-10 equal portions. On a lightly floured surface, roll out one portion of dough very thinly, into an 8-inch circle. Use an 8-inch plate or cake pan as a guide to cut a perfect circle, reserving the scraps. Repeat with remaining dough and scraps.
Step 7: Carefully transfer each rolled-out dough circle to a prepared baking sheet. Bake one or two at a time for 5-7 minutes, or until golden brown and slightly firm. Let the baked layers cool completely on a wire rack. Bake the re-rolled scraps for decoration.
Step 8: In a large bowl, combine the very cold sour cream, heavy cream, powdered sugar, and vanilla extract. Beat with an electric mixer on medium-high speed until thick, fluffy, and well combined. Be careful not to overbeat.
Step 9: Place one cooled cake layer on your serving plate or cake stand. Spread about 1/3 to 1/2 cup of the sour cream frosting evenly over the layer. Repeat with the remaining cake layers, stacking them one by one.
Step 10: Once all layers are stacked and frosted, spread the remaining frosting over the top and sides of the entire cake. Crush the baked cake scraps finely using a food processor or by hand and gently press the crushed crumbs onto the top and sides of the cake.
Step 11: Cover the cake loosely with plastic wrap and refrigerate for at least 12-24 hours. This allows the cake layers to soften and absorb the creamy frosting.
Step 12: Before serving, let the Russian Honey Cake Medovik sit at room temperature for about 30 minutes to an hour to allow the flavors to truly bloom. Slice with a sharp knife and enjoy this incredible creation!