Lightly season Steaks on both sides with the Salt, Pepper, and Garlic Plus. In a large fry pan on medium-high heat, add Butter and Oil. When frothing has slowed, (about 3 minutes), add the Steaks. Brown the Steaks on both sides, 3 minutes per side. Transfer the Steaks to a plate and set aside, and cover.
Add more Oil to fry pan, then add Onions, sauté for 5 minutes. Add Butter, allow to melt, add Mushrooms, sauté 10 minutes more.
Reduce heat to medium, make a well in centre of pan, add a little Oil if required. Add Tomato Paste saute for 2 minutes. Add the Garlic, saute for 30 seconds. Deglaze with Wine, allow Wine to mostly reduce.
Add Mustard, Salt, Pepper, Worcestershire and the reduced Chicken Stock. Simmer to 5 minutes. Add Cream, mix well.
Return the Steaks to the fry pan, covering all sides of Steaks with sauce. Bring to a simmer, cover simmer for 4 minutes.
To serve, place a Steak on each plate and pour the Sauce over the Steak.