burn something to a crisp
US /bɜrn ˈsʌm.θɪŋ tu ə krɪsp/
UK /bɜrn ˈsʌm.θɪŋ tu ə krɪsp/

1.
to burn something so much that it becomes very dry, hard, and often black
:
•
I left the pizza in the oven too long and burned it to a crisp.
•
The toast was burned to a crisp, completely black and inedible.