Heat the oil in a large cast iron skillet over medium heat, add the garlic & onions, saute', stir frequently and cook for 20 minutes. Add the stock, raise the ehat to high and cook for approx. 7 minutes until the liquid is reduced by 1/2. Add the mustard, honey, & vinegar, reduce heat to med-low and simmer for 10-15 minutes. Remove from heat and allow to sit for 10-15 minutes. Serve warm but not hot. * Note: This is atraditional sauce that is used with many dishes. It is great with vegetables, better with meats, and will keep refrigerated for 5-7 days or frozen for 3-4 months.