Preheat oven to 350°F. Grease or spray the bottom and sides of a 13x 9-inch baking pan.
In a large bowl, place cake mix, butter, cream cheese and egg. Using an electric mixer on medium speed, beat 2 to 3 minutes, stopping once to scrape down the bowl. Loosely wrap about 1/3 of the dough in plastic wrap and refrigerate. Press remaining dough into the bottom of the prepared pan. Bake 10 minutes.
Remove pan from oven and top dough with spoonfuls of dulce de leche. Return to hot oven for 5 minutes, then gently spread dulce de leche to cover dough. Crumble remaining dough from the fridge evenly over dulce de leche.
Return pan to oven and bake 24 to 28 minutes, until top is light golden brown. Let cool on a rack. Cut into bars. Dust with powdered sugar.