We had a similar problem* and Googled for solutions, which were many. The one that worked for us was a heavy sprinkle of baking soda and a spray bottle of vinegar to produce that wonderful 3rd-grade-science-experiment fizz. Liberally douse and allow the fizz to subside, then wait another 15-20 minutes before using a plastic utensil with a flat edge to scrape off. Was very surprised how well this worked.
*Don’t ask, but somehow one of the burners turned itself on 
while a small rubber-backed throw rug was atop. No one noticed until there was smoke and an awful smell. What a melted mess. And don’t ask why there was a rug on top of the stove.