A Witch's Guide to Fake Dating a Demon by Sarah Hawley

Mariel Spark knows not to trust a demon, especially one that wants her soul, but what's a witch to do when he won't leave her side—and she kind of doesn't want him to?
Mariel Spark is prophesied to be the most powerful witch seen in centuries of the famed Spark family, but to the displeasure of her mother, she prefers baking to brewing potions and gardening to casting hexes. When a spell to summon flour goes very wrong, Mariel finds herself staring down a demon—one she inadvertently summoned for a soul bargain.
Ozroth the Ruthless is a legend among demons. Powerful and merciless, he drives hard bargains to collect mortal souls. But his reputation has suffered ever since a bargain went awry—if he can strike a bargain with Mariel, he will earn back his deadly reputation. Ozroth can't leave Mariel's side until they complete a bargain, which she refuses to do (turns out some humans are attached to their souls).

But...