Start making the Potato cake with rusks and condensed milk. Transfer the crushed rusks to a deep bowl. Add cocoa powder and stir. Add condensed milk. Mix the rusks with condensed milk and add softened butter. It is better to mix the ingredients with your hands until the mass becomes sticky and stops crumbling.
Form a "potato" from breadcrumbs with condensed milk. Separate an equal amount of the mass and roll it into a ball. Then give it an oval shape. Roll the cake in breadcrumbs intended for breading. Put the cakes in the refrigerator for 30 minutes. The butter should set, harden slightly, and the cakes will hold their shape better.