Prepare a 9 x 13 cake according to the directions on the box. Once done, allow cake to cool completely.
Using a straw, or similar sized item ( I've used chopsticks before too! hehe) poke holes about every inch, forming rows of pokes.
You need holes to be fairly big so that condensed milk has plenty of room to get down and soak the cake.
Pour 1/2 of the can of sweetened condensed milk over the entire cake. Use a spatula to smooth over cake. Set aside.
Next, in a large bowl, combine the ricotta, mascarpone and vanilla ad remaining condensed milk, and beat until smooth.
Add in the powdered sugar and continue to mix until well combined. Start with 2 cups, and if you would like your frosting to be a little thicker, add in that 3rd cup.
Spread the cannoli topping evenly over the top of your cake. Sprinkle with mini chocolate chips and some powdered sugar.
Serve right away, or cover and place in the refrigerator until ready to use.