[Leo, it's like you're psychic. Because... Sebastian nods thoughtfully, as if this is completely expected news, and immediately asks:]
Then, would you please teach me? [And before Leo has a chance to protest or even answer one way or another, Sebastian holds up a hand and continues.] Please allow me to explain: my request is not for the device to simply be fixed. I researched the issue when it broke, and I am confident I could now handle it myself... but using the method I looked up, my estimation is that I would need to spend a few hours on it.
[Now if he were to use his unfair demon powers he could probably just snap his fingers and the mixer would be good as new, but that's neither here nor there.]
You and Mr Stark are, I believe, on a far more advanced level than any textbook in the local library. [Tl;dr: it's not enough to be able to just fix it, I wanna be the very best like no one ever was.]