In a large mixing bowl, sift together 2 cups of all-purpose flour and 1 cup of granulated sugar to ensure even distribution and eliminate lumps. Set aside.

In a separate bowl, combine 0.5 cup of unsalted butter and 0.5 cup of margarine using a handheld mixer. Beat until creamy and light in color, about 2-3 minutes.

Make a well in the center of the flour mixture and add 2 large eggs, 3 tablespoons of mayonnaise, and 1 teaspoon of baking powder. Mix until a soft, slightly sticky dough forms.

Divide the dough into small pieces, roughly the size of a walnut. Preheat your oreshki mold on the stovetop over medium heat and lightly grease.

Fill each cavity with dough, pressing it firmly while leaving space for expansion. Close the mold and cook for about 1½ to 3 minutes on each side, until golden brown.

After cooking, carefully remove the cookie halves and place them on a cooling rack.

Once cooled, fill half of the cookie shells with dulce de leche and place another half on top to create the walnut shape. Press gently to adhere.

For best flavor, allow the assembled cookies to sit for at least 1 hour or ideally overnight.