slave over (something)
To spend a lot of time working strenuously and continuously on or at something. I know you were slaving over your project for weeks, so I'm delighted to hear that you got such great marks on it from your teachers. I slave over a computer for eight hours a day, so the last thing I want to do when I get home is sit in front of another one. Kids, I spent nearly three hours slaving over a hot stove getting this dinner ready, so by God, you're going to eat it!
slave over something
Fig. to stand over something, working at it very hard, typically cooking over a hot stove. I've been slaving over this hot stove for hours to cook this meal! Ted slaved over his special dessert for hours.