Preheat your oven to 350°F and grease up that 9x13-inch pan real good.
Mix up the cake like the box says, then pour it into your pan.
Bake for 28 to 32 minutes until a toothpick comes out clean, then cool 10 minutes.
Poke holes all over the warm cake with your wooden spoon handle about 1 inch apart.
Pour the sweetened condensed milk slowly over everything, filling up all those holes you made.
Let the cake cool down completely for about 1 hour before you frost it.
Beat the cream cheese and butter together for 2 minutes until it's nice and fluffy.
Add the sugar, vanilla, and salt, then beat until it's all smooth and creamy.
Spread the frosting over your cooled cake with a spatula or butter knife.
Sprinkle those mini chocolate chips on top and press them down just a little bit.
Put the cake in the fridge for at least 2 hours so everything sets up perfectly.
Cut it into squares and serve it cold right from the fridge for the best taste.