"A decadent cake with three distinct layers: walnut, raisin, poppy seed. I am not a big fan of cake. But, I can devour this cake in one sitting! The butter and condensed milk icing makes this cake irresistibly moist."
Preheat oven to 350 degrees F (175 degrees C). Grease and flour three 9-inch round cake pans.
Beat sugar and eggs together in a bowl using an electric mixer for 5 minutes.
Sift flour and baking soda together in another bowl. Beat into the egg and sugar mixture gradually, alternating with sour cream, until a smooth batter forms. Divide batter equally between 3 bowls.
Fold walnuts into the first bowl, raisins into the second bowl, and poppy seeds to the third. Pour each bowl into its own separate cake pan.
Bake cakes in the preheated oven until a toothpick inserted into the centers comes out clean, 20 to 30 minutes.
Let cakes cool in pans for a few minutes. Remove from pans carefully; let cool completely, at least 30 minutes.
Beat 3/4 cup plus 2 tablespoons butter in a bowl using an electric mixer until creamy. Add condensed milk slowly, mixing with a fork or spatula in a clockwise motion. Spread a couple of tablespoons of buttercream onto a large cake plate.
Place one of the cakes onto the butter cream on the cake plate. Spread another few tablespoons buttercream over the cake and lay another cake on top. Repeat with the remaining cake and cover top and sides with remaining buttercream. Decorate as desired.