Add 1 tablespoon olive oil to the pan and add the onion, carrots, celery, garlic, and mushrooms. Cook until the mixture is deep golden brown, about 5 minutes. Turn off the heat and add the brandy and add 2 cups of the stock. Stir, scrape the bottom of the pan, and turn the heat to medium-high. Add paprika, thyme and Worcestershire sauce, cook to reduce the liquid by about a third, 3 to 4 minutes.
In a small pitcher, make a slurry by mixing the remaining 1/4 cup stock and the cornstarch with a fork. Pour the slurry into the skillet and cook until the sauce thickens, about 1 to 2 minutes. Turn off the heat. Stir in the sour cream and Dijon. Add the beef and stir over low heat until the mixture is nice and piping hot. Taste and adjust seasonings as you like.
Serve over egg noodles