How do I clean this silicone tray? I use this silicone muffin pan to cook things in the oven. It's supposed to be non-stick, but actually food sticks to it quite a lot.

Often I can just scrape dried food off with my fingers, but it's gradually building up brown stains and crusts that I can't remove even by scrubbing hard with a scourer. Is there some kind of trick to make it spotlessly clean again?
Try to put your silicon tray in boiling water for 3 to 5 minutes. I had the exact same problem and it worked fine for me.