Here's what I've tried:

{
  description = "My NixOS configuration.";
  inputs = {
 
    nixos.url = "nixpkgs/nixos-unstable";
    jupyterWith.url = "github:tweag/jupyterWith";
  
  };
  outputs = { self, nixos,  jupyterWith}: {
     nixosConfigurations.jon-laptop = nixos.lib.nixosSystem {
       system = "x86_64-linux";
       modules = [ ./configuration.nix
                   jupyterWith.jupyterlabWith { kernels = [
                                                  (jupyterWith.kernels.iPythonWith {
                                                    name = "python";
                                                    packages = p: with p; [ pandas ];
                                                  })
                                                  (jupyterWith.kernels.iRWith {
                                                    name = "R";
                                                    packages = p: with p; [ ggplot2 ];
                                                  })
                                                ]; }
               
                   }
                 ];
     };
  };
}