Also, it had to be something quick and simple, so even though my last two tries failed big time, I went for brownies in a mug.
This time, I beat the egg with an electric mixer first and used melted butter instead of oil. Unfortunately, I didn't have dark chocolate at hand, but was hoping a Sport szelet (rum flavored, dense chocolate bar) would suffice. It did.
The world now seems a whole lot nicer :D