Braising in apple juice helps tame the bitterness of cooked endive.
1. Melt butter in skillet over medium-high heat. Place endives cut-side-down in skillet, and cook 8 minutes, or until browned. Transfer to plate, and add leek to pan. Cook 1 minute, then stir in vinegar. Simmer 2 minutes. Add juice, broth, thyme, and endives cut-side up, and bring to a simmer. Cover, reduce heat to low, and simmer 5 minutes.
2. Uncover; increase heat to medium-high. Simmer 10 minutes. Transfer endives to platter. Stir mustard and cream into liquid. Simmer 4 minutes, or until thickened. Serve endives garnished with pan sauce, nuts, and parsley.