Peel the onions, cut in half and slice thinly. Heat the oil in a saucepan and saute the onions until starting to colour.
Crush, peel and finely chop the garlic. Add to the pan and cook until the onions are lightly golden.
Add the vinegar, wine, sugar, bay leaf, peppercorns, beef stock, tomato paste and thyme to the pan. Bring to the boil. Reduce the heat and simmer until the sauce is reduced by half or to the preferred consistency.
Strain the sauce. Season to taste.
Cool then refrigerate until ready to use.
Serve hot, with red meat. Only heat the amount required for a meal leaving the remaining sauce in the fridge or freeze if preferred. The sauce will keep in the fridge for 7 – 10 days. Makes about 1 ½ cups