4 ounces Tomme de Savoie cheese, grated (1 1/2 cups)
4 ounces GruyÈre cheese, grated (1 1/2 cups)
Put the endives in a deep skillet that holds them comfortably in a single layer. Add the chicken stock, lemon juice and salt. Cover the endives with a round of parchment paper, make a small hole in the center of the paper and bring to a boil. Reduce the heat and simmer, turning occasionally, until the endives are very tender when pierced, about 30 minutes. Remove the endives as they are done and pat thoroughly dry.
Preheat the broiler. In the same skillet, cook the bacon over moderately high heat until lightly browned, about 3 minutes. Add the endives, reduce the heat to moderate and cook, turning occasionally, until evenly browned, about 10 minutes.
Transfer the endives and bacon to a gratin dish and sprinkle with the grated cheese. Broil for about 5 minutes, turning the dish to brown the cheese evenly. Serve immediately.
The gratin can be prepared through Step 2 and refrigerated overnight. Reheat the endives before proceeding.