For the sauce, melt the butter in a medium-sized saucepan, add the minced vegetables, and fry over a medium-high heat until they are lightly browned. Add the brandy and, as soon as it has evaporated, add 3 3/4 cups (900 ml) of the chicken stock, the wine, bay leaf, and thyme. Bring to a boil, then lower the heat and let simmer for 30 minutes. Strain the stock through a fine sieve into a wide saute pan. Bring to a boil and boil rapidly until reduced to about 1 1/2 cups (350 ml) and well concentrated in flavor.