Using butter knife, spread 1 tsp dulce de leche on back side of each maria cookie. Arrange cookies on plastic-lined baking tray.
Using 2-oz ice cream scoop, or heaping tablespoon measure, spoon ice cream on half of cookies. Top ice cream with remaining cookies to form mini ice cream sandwiches; press down gently. Transfer sheet to freezer; freeze until firm, about 1 hour.
Using butter knife, trim edges of cookies to smooth edges. Place nuts, candy bars and/or sprinkles on separate plates. Roll edges of cookies in toppings. Serve immediately.