Heat the butter or oil in a large skillet over medium-high heat. Add the veal or beef cubes and cook until browned on all sides, about 5-7 minutes. Remove the meat from the skillet and set aside.
In the same skillet, add the chopped onion and cook until translucent, about 3-4 minutes. Add the minced garlic and cook for another 1 minute.
Pour in the beef or vegetable broth, scraping up any browned bits from the bottom of the pan. Allow the liquid to simmer for about 2 minutes.
Stir in the heavy cream and Dijon mustard. If you prefer a thicker sauce, mix the flour with a small amount of water to make a slurry and stir it into the sauce. Simmer for 3-5 minutes, or until the sauce has thickened to your liking.
Add the browned meat back into the skillet, stirring to coat it with the sauce. Cook for an additional 5-7 minutes, or until the meat is tender and the flavors are well combined.
Season with salt and pepper to taste. Garnish with chopped fresh parsley or chives.
Enjoy your meal!