Slice the veal tenderloin against the grain into thin slices about 2 inches (5 centimeters) long and 1/3 inch (1 centimeter) thick. Toss with the flour.
Place a large saucepan over medium heat. Add 2 tablespoons (28 grams) of the butter.
Once the butter has melted, add the veal slices, sprinkle with salt and pepper, and cook, stirring occasionally, just until browned on all sides.
Remove the veal to a plate and set aside.
Add the remaining 1 tablespoon (14 grams) butter to the pan.
Once melted, add the sliced mushrooms and onion. Cook, stirring occasionally, until the mushrooms are starting to brown and the onions starting to soften.
Stir in the garlic and cook until just fragrant, 30 seconds to 1 minute.
Pour in the white wine, scraping the bottom of the pan to remove any browned pieces.
Simmer until the wine has reduced by half.
Place the cornstarch in a medium bowl. Slowly add the vegetable stock while whisking to incorporate the cornstarch. Whisk in the cream.
Reduce heat to medium low. Add the cream/vegetable stock/cornstarch mixture and bring to a simmer.
Stir in the set-aside veal, season with salt and pepper, and continue to simmer, stirring occasionally just until the sauce has thickened and the veal has cooked through.
Sprinkle with the chopped parsley and serve immediately while still hot with desired sides.