Heat the olive oil in a large skillet over medium-high heat. Saute the onions with the salt until well caramelized, 8 to 10 minutes. Add the garlic and saute 2 to 3 minutes longer to soften.
Add the jalapeno, tomatoes, olives and vinegar. Bring to a boil. Pour in the chicken stock, bring back to a boil and simmer 10 minutes. Break the butter into a few pieces and whisk into the sauce. Remove from the heat.
Heat the vegetable oil in a large skillet over high heat. Add liver and cook for 3 minutes per side. Then pour in the sauce, bring to a boil and remove from the heat. Serve immediately.
c.1997, M.S. Milliken & S. Feniger, all rights reserved