Turn on the oven to preheat to 180 degrees. If the dough is frozen, then it must be removed from the freezer and allowed to thaw.
Melt the butter in a large skillet over medium heat, pour the lettuce, leeks and shallots into the pan, sprinkle with sugar, salt, pepper and nutmeg, cook, stirring occasionally, until soft, about 8 minutes.
Reduce heat under the pan and add cream cheese, stir, and then add all the rest of the cheese, mix well.
In a large bowl, combine eggs and cream and beat lightly. Gradually, while stirring, add this mixture to the onion mass in a frying pan. Stir well and put out the fire.
Roll out the dough into a circle with a diameter of about 35 cm, wrap it on a rolling pin, and put in a heat-resistant mold with a diameter of 22 cm, forming the sides of the dough.
Pour the onion mixture into the prepared cake and put in a preheated oven, bake the cake for about 40 minutes, until golden brown. Remove the finished cake from the oven and chill on a wire rack for 10-15 minutes.