Melt the butter in a large skillet. Add the sugar and 1/2 tablespoon of the lemon juice and cook over moderate heat until the sugar starts to caramelize, about 3 minutes. Add the endives, stir to coat and cook, stirring occasionally, until softened, about 5 minutes. Raise the heat to moderately high and cook until any liquid in the pan has evaporated and the endives are lightly caramelized, about 7 minutes. Add the remaining 1 tablespoon of lemon juice and season with salt and pepper. Remove from the heat.