Lightly pound each steak to even thickness. Season both sides with salt and pepper. Coat in flour, shaking off any excess.
Heat the clarified butter in a large pan over medium-high heat. Sear the steaks for 1 minute on each side. Reduce heat to medium and continue cooking to your preferred doneness: rare (50-55°C / 122-131°F), medium (60-65°C / 140-149°F), or well done (70°C / 158°F+). Transfer to a warm plate.
Slice the 3 onions into rings and chop the garlic clove finely. In the same pan, fry the onions and garlic over medium heat for 2-3 minutes until softened.
Sprinkle 1 tablespoon flour over the onions and garlic. Stir well with a spoon to distribute evenly.
Pour in the red wine and meat stock, scraping up any browned bits from the pan. Stir in 1 tablespoon mustard and ½ tablespoon marjoram. Season to taste with salt and pepper. Simmer over medium heat for 5-8 minutes until the sauce turns brownish.
Return the steaks to the pan and heat through for 1-2 minutes. Serve immediately.