Allspice is, apparently, the national spice of Jamaica. Freshly ground allspice will be more aromatic, of course, but already ground is perfectly fine; though you may want to add an additional pinch to the mix. Your choice of chile pepper will determine the spiciness of this dish, or omit it entirely.
2 large bunches greens
2 T butter
2 T vegetable oil
1 small onion, finely diced
1/4 t freshly ground allspice, or to taste
salt and pepper
1 to 2 dashes Angostura bitters, or 1/2 t Worcestershire sauce
1 small chile pepper, stemmed, seeded, minced, or 1/4 t red pepper flakes or cayenne
2 t lemon or lime juice, optional
1. Wash (and stem) greens. Put them in a large pot with the water that clings to the leaves and cook over medium heat until wilted. Add some water if you think they are starting to stick the to pot. Drain, if necessary. Cool enough to handle and roughly chop. Set aside.
2. Heat the butter and oil in a skillet over medium heat until the butter is melted and saute the onion for about 5 minutes, stirring occasionally. Add the chopped greens along with the allspice, salt, pepper, bitters and chile. Stir well, cover, if you like, and cook the mixture over low heat for about 10 minutes. Taste for seasoning, sprinkle with lemon or lime juice and serve hot.