Eliminating re-implementation of methods from the built class in Builder, while keeping it with nested calling

I have a class that has to be checked for being set for all of the variables, while more variables that must be set could be added:

class A{
   setVar1();
   setVar2();
   setVar3();
}

I have to check that all three sets were called before building it. How can I create a Builder that:

A. won't have to re-call the above methods again (like implementing inside builder another setVar1() setVar2() which will call those from A - this is a hell for future maintenance to me to implement each of those setters twice). So bad example for me here would be:

class ABuilder{
   build(){...}
   builderSetVar1(){...} //HELL NO!
   builderSetVar2(){...} //NO NO NO!!!
   ...
}

B. Will check before building that all must have members are set (the user of the package, won't be able to have incomplete A)

C. Will allow nested one-line building of A (Builder...SetVar1(...)....SetVar2(...).build())

Is it even possible to achieve all of those three goals? I tried too many possibilities and in every solution

All in object oriented.