Recursive call to a monotonic function with an IIFE stop or creating add function that returns unknown num of functions for adding the next number

Question

I had a question in an interview:

how to implement add(1)(2)(3).....();

Below is the case for 3 instances. But how to stretch it for more instances? The stop condition for the recursion is the function with an empty argument (IIFE)

function add(a){
   return function add(b){
     return function add(c){
       return a+ b+ c;
     }
   }
}