Sweat the onion: In a medium flameproof casserole over medium heat, melt the butter. Add the onion to the pot and let it sweat for about 8 minutes, until soft but not browned at all (this is a ...

For the topping, heat the butter in a large skillet over medium heat; add the onion and cook until softened but not browned, about 5 to 7 minutes, stirring occasionally. Add the thyme, salt, black ...