Add in butter and margarine. Use a handheld mixer to combine the ingredients until you have a smooth, even consistency.
Make a little hole in the middle of the flour mixture. Then, add the eggs, mayo and baking powder into it.
Use your handheld mixer to beat the ingredients together completely. Your dough should be soft and a little sticky.
Place small pieces of dough inside each metal form of an oreshki mold. When using a stove top, cook until golden brown. Flip the pan over and cook the other side. FYI: Each side can take 1½ to 3 minutes depending on the thickness of your mold. Make sure to check the instructions on the box!
Let the cookies cool. Then, break off the access dough that seeped out of the molds and cooked to the inside of the pan.
Fill each mold with dulce de leche. Then, place another mold on top to make an walnut shape.