Break and crack the carcasses. In a large stockpot, heat the vegetable oil. Season the bones with salt and pepper. Add the bones to the pot and brown for about 10 minutes, stirring often. Add the onions, carrots, celery, garlic, and bay leaves. Season the mixture with salt. Cook until the vegetables are soft, about 5 minutes, stirring often. Add the wine and tomato paste and stir to mix. Cook for 5 minutes, stirring occasionally. Add the water. Put the thyme, parsley sprigs, and peppercorns in a piece of cheesecloth, tie it together with kitchen twine, and add it to the mixture. Bring the mixture to a boil. Skim off any cloudy scum that rises to the surface. Reduce the heat to medium and simmer, uncovered, for 3 hours. Strain through a fine-mesh strainer and cool. Refrigerate overnight and remove any congealed fat from the surface. The stock can be stored in the freezer for 1 month.
Yield: about 6 cups