Whisk together spices, 2 teaspoons salt, 1 teaspoon pepper, and oil in a small bowl.
Pat hens dry and stuff cavity of each with 1/3 cup haroseth.
Place hens in a large flameproof roasting pan and rub all over with spice mixture, including underneath skin of breast meat (loosen skin gently with your fingers). Tuck wings underneath body, then secure legs together with a wooden pick or tie with kitchen string.
Roast hens 20 minutes, then brush with pan drippings. Continue to roast, basting every 10 minutes, until juices run clear when a thigh is pierced, 25 to 30 minutes more (45 to 50 minutes total).
Transfer hens to a cutting board.
Straddle roasting pan across 2 burners and boil drippings, scraping up brown bits, 2 minutes. Carefully add Sherry (it may ignite) and boil 2 minutes (or until flames subside).
Add water and boil, stirring, until sauce is slightly thickened and reduced to about 1 1/2 cups, 4 to 5 minutes.
Transfer sauce to a measuring cup and let stand 1 minute, then skim off fat (or use a fat separator).
Serve hens, halved if desired, with sauce on the side.
