I would take the plate out and rinse and scrub with dishsoap, then spray the microwave from top to bottom with a de-greasor like Ecover (because its non-toxic) and use a dab of baking soda on a sponge to scrub the stuff that doesn't wipe away, and a rag to shine it. *Here's an extra hint: put a bowl of baking soda in microwave to ensure freshness and deoderizing between uses.