To Burn
To Scorch, To Char
transitive verb, godan verb
Remember how 焦げる means "to get burned"? 焦がす is the transitive version, so this time someone is actively doing the burning, making it to burn, to scorch, or to char.
焦がす means to burn the surface of something, usually blackening it to some degree. Unlike 焦げる, it can be for both intentional burning (a nice crème brûlée) and accidental burning (leaving bread in the toaster too long, scorching your sleeve on the stove).
The reading comes from 焦げる, so if you know that you know this word as well.
いつもトーストを真っ黒に焦がしてしまう。
I always burn my toast completely black.