The single recording button always pauses/resumes. This is by popular demand; it used to work the way you are describing it.
To restart the recording, you can reselect the song. If you are showing the song list in your layout, you can select the same song in the list again. If you are not showing the song list, you will have to move to the next or previous song and back again.
Alternatively, you can add the Recording Controls to your layout. Then you can tap the rewind button in the recording controls to restart the recording.