Creating a LaTeX Command with Conditional Arguments for Different Behaviors

How can I define a function call \StepFrame that accepts default arguments, as well as optional arguments for more complex behavior? I would like to define a LaTeX command \StepFrame that behaves differently depending on the number of arguments passed to it. Specifically, I want:

1. A default case, where the command is called with two arguments (title and image file), and it generates a frame with a single image.
2. An optional case, where the command is called with three arguments (title, main image, and overlay image), and it generates a frame with the second image overlaid on the first image.

Here's a basic version of my code:

\documentclass{beamer}

\newcommand{\StepFrame}[2]
{   
    
    %% default case:
    \begin{frame}{#1}
        \includegraphics[width=\textwidth]{#2}
    \end{frame}
    
    %% optinal case:
    %\begin{frame}{#1}
    %   \includegraphics[width=\textwidth]{example-image}\llap{\includegraphics[width=0.4\textwidth]{example-image}}
    %\end{frame}
}

\begin{document}
    
    %% call the function \StepFrame with default arguments (single image)
    \StepFrame{my title 1}{example-image}
    \StepFrame{my title 2}{example-image}
    \StepFrame{my title 3}{example-image}
    
    %% call the function \StepFrame with optional arguments (image inside another image)
    %\StepFrame{my title 4}{example-image}{example-image-b}
    %\StepFrame{my title 5}{example-image}{example-image-b}
    %\StepFrame{my title 6}{example-image}{example-image-b}

\end{document}