In a mixing bowl, combine all the BBQMarinating sauce ingredients until well combined. Add chicken and coat it well with the marinating sauce, then marinate for at least 30 minutes.
In a pan over medium heat, melt unsalted butter then saute garlic, onion, and mushroom until fragrant. Add cooking cream and milk then stir. Season it with salt, black pepper, sugar, mushroom seasoning, italian herbs, and nutmeg. Cook and stir until well combined and the sauce is thickened. Turn off the heat and set aside.
In another pan, grill the marinated chicken thigh fillet. Occasionally brushing it with the remaining marinade sauce and cook until both side of the chicken is cooked.
Place the chicken steak into a plate then pour mushroom sauce over the steak. Serve the chicken steak with boiled vegetable mix and french fries. The chicken steak with mushroom sauce are ready to serve. Enjoy!