How to Make It
Preheat the broiler and position a rack 6 inches from the heat.
In a large, deep ovenproof skillet, melt the butter in 1 tablespoon of the olive oil. Add the leeks, season with salt and pepper and cook over moderate heat, turning, until golden, about 5 minutes. Add the remaining 1 tablespoon of olive oil along with the endives, garlic and thyme sprigs and cook, turning, until the endives are golden, about 3 minutes. Add the broth and bring to a simmer. Cover and cook, stirring occasionally, until the vegetables are almost tender, about 5 minutes. Uncover and cook until almost all of the broth has evaporated, about 3 minutes.
Discard the thyme sprigs. Sprinkle the cheese over the endives and leeks. Broil for 2 to 3 minutes, until the cheese melts. Garnish with thyme leaves and serve warm.