Best way to have a recurring toast show at regular intervals?

I want to create a store app that shows a toast message to the user at regular intervals (say, every 15 min or 30 min). The toast message can vary (for example, displays the system time). My app won't be on the lock screen and needs to show the toast even when my main app is closed.

What's the best way to handle this? BackgroundTask? BackgroundWorker? Other?