Mix the milk, cake mix, cream cheese and sugar together with a mixer. Mix until smooth.
Add the Cool Whip and mix until combined.
Add the sprinkles and brownies (you can use store-bought or homemade brownies) and mix until combined.
Stir in the chocolate sundae syrup. Stirring a little less will give more of a ribbon of chocolate to the ice cream. Stirring more will make it more uniformly chocolatey.