Making the D1 sauce: Heat the oil in a large saucepan over medium-high heat. Add the onions and cook, stirring, for 3 minutes, or until just beginning to color. Stir in the carrots, garlic, and cracked pepper and cook stirring, for 2 minutes, or until the carrots have taken on some color. Stir in the vinegar and Worcestershire and, using a heatproof spatula, scrape the browned bits from the bottom of the pan. Cook, stirring occasionally, for about 5 minutes, or until the liquid has reduced by half. Add the stock, ketchup, and brown sugar and bring to a boil. Immediately lower the heat and simmer for 5 minutes. Whisking constantly, add the cornstarch mixture in a slow, steady stream. Cook, stirring constantly, for 5 minutes, or until quite thick. Remove the sauce from the heat and pour into a blender. Holding the lid down with a folded kitchen towel to prevent a steam explosion, process to a smooth puree. Season with salt to taste. Use as directed in a specific recipe, or store, tightly covered and refrigerated, for up to 1 week. Reheat before using.