Preheat the oven to 180 ° C (convection 170 ° C). Beat the sugar and eggs until foamy, stir in the butter, flour, cocoa and baking soda. Fold in the sour cream. Grease a bundt pan and sprinkle thinly with breadcrumbs.
Pour the dough into the mold and bake for about 50 minutes. Then take it out of the oven and let it cool down in the tin. Turn the cake out.
For the glaze, melt the two chocolates separately. Cover the cake completely with the milk glaze, then decorate with the white glaze in strips.