Multithreading and function recursion

Question

I haven't done multi-threading before, so I need a bit of help with this.
I have a form with a button. When user clicks on a button for the first time, a recursive function is called. When a certain condition in the function is true, I want the function to wait where it's at for the next button click.

An example:

void ButtonClick(object sender, EventArgs e)
{
    if (running)
    {
        //notify the thread (the recursive function) to continue
    }
    else functionCall(0);
}

void functionCall(int num)
{
    if (num % 2 == 0)
    {
        displaySomething();
        //wait
    }
    functionCall(num + 1);
}

How would I do this?