Preheat oven to 350 degrees F (176 C) and spray the cake pans with non stick baking sprayUsing a standing or hand mixer, beat the cake mix, butter, milk and eggs until combined
Remove the tops from the cakes to make into a even layer. Using one of the cake layers are the bottom, pipe a thick ring around the top of the cake twice. Spoon about 3⁄4 C of dulce de leche into the middle of the frosting rings and smooth
Place second cake layer on top and pipe two more rings of frosting around the edge. Spoon 3⁄4 C of frosting into the center of the frosting rings. Place last cake layer on top and frost entire cake. Smooth.
Scoop dulce de leche into a bowl and microwave for 30 sec. Pour the dulce de leche into the disposable piping bag and pipe drips along the edge of the cake. Pipe frosting dollops around the top of the cake.