Place the tongue in a medium saucepan and add water - add enough to cover. Add the white onion, carrot, celery, bay leaves, clove, salt and black peppercorns. Bring to a boil, reduce to a simmer and cook, uncovered, 1 1/2 to 2 hours, until tender. Transfer the tongue to a cutting board, cover with a damp towel and set aside to cool. Strain and reserve the stock.
Peel and discard the tongue's skin. Cut the meat into 3 x 1/2-inch julienne strips.
Melt the butter in a large saucepan over medium-high heat. Saute the red onion until well browned, about 10 minutes. Stir in the garlic and saute an additional 2 minutes. Add the tomatoes and jalapenos and saute 2 minutes longer. Then add the tongue and reserved stock. Simmer 8 minutes. Sprinkle in the oregano, and remove from the heat. Serve over white rice.
c.1997, M.S. Milliken & S. Feniger, all rights reserved