Veloute sauce is one of the 5 French mother sauces listed by Auguste Escoffier made with a blond roux and a white stock made from either chicken, veal, or fish.
Melt the butter in a saucepan over medium heat.
Then add the diced onion, celery, and carrot. Cook the vegetables until they start to sweat, but don't brown them.
Sprinkle the flour over the vegetables to make a roux, lower the heat, and stir for 2 - 3 minutes.
Increase the heat and slowly add the stock, whisking vigorously until it comes to a boil.
Reduce the heat to a simmer and add the bay leaf, fresh thyme, and parsley. Let simmer for at least 10 to 15 minutes, or up to an hour.
Strain through a mesh cloth or a fine sieve. Season with salt and pepper. Adjust seasoning if needed.
Serve right away or dot with butter and refrigerate in an air-tight container for up to 1 week.