Adding text with fontawesome in button WPF

I'm trying to generate some text underneath a fontawesome icon inside WPF:

<Button HorizontalAlignment="Left" Height="40" Width="40" FontFamily="Arial Black" Foreground="White" Margin="5,30,0,0" fa:Awesome.Content="Folder">
    <StackPanel>
        <TextBlock>
            My Folders
        </TextBlock>
    </StackPanel>
</Button>

The problem now is that it only shows "My Folders" and the fontawesome icon is gone - I can confirm that the icon works (when I remove the textblock it displays it).