public Form1()
{
    InitializeComponent();
    CheckForIllegalCrossThreadCalls = true;
}

async Task DelayAsync()
{
    // GUI context is captured here (right before the following await)
    await Task.Delay(3000);//.ConfigureAwait(false);
    // As no  code follows the preceding await, there is no continuation that uses the captured GUI context.
}

private async void Button1_Click(object sender, EventArgs e)
{
    Task t = DelayAsync();

    t.Wait();
}