Diagnosis
That's carbonized grease and food particles. The smell is them burning off, which can affect food taste.
How to Fix It
Unplug and cool completely. Fill the basket with 2 cups water and 1 tbsp baking soda or lemon juice. Run the unit at 400°F for 10 minutes. The steam will loosen debris. Let cool, then wipe the element and interior with a damp, non-abrasive cloth. Use a soft-bristled brush for stubborn spots.
If That Didn't Work
For heavy buildup, use a dedicated degreaser spray. Spray on a cloth first, not directly into the unit. Wipe the element carefully. Never submerge the base.
Heads Up
Never use metal scouring pads or sharp objects on the heating element. You can damage the protective sheath and cause a short.