I always burn my toast completely black.
You know that 焦げる is "to be burned" or "to get burned." This word however is when you're doing the burning, making it to burn or to scorch. You know this because when it comes to burning, you pull out all the stops. You use lots of gas (がす) to burn whatever it is you burn.
The reading comes from 焦げる, so if you know that you know this word as well.