Can we have a function of a complex variable whose real and imaginary parts cannot be represented in cartesian Mongé $ z= F(x,y) $ form, but can only be represented as a parametrized surface $$ (x,y,z)= f(u,v), g(u,v),h(u,v))\quad ? $$
If not possible, why not? and if it is possible, please give some illustrative examples of such non-orthogonal parameterized cases.
For example for $ w=z^3$ the monkey saddle parts are both of Cartesian Mongé form only.