Start by boiling the potatoes. Place the quartered potatoes in a pot, cover them with cold water, and add a pinch of salt. Bring to a boil and cook for 15-20 minutes until fork-tender.
While the potatoes are boiling, prepare the chicken and steak. Season both proteins with salt, pepper, olive oil, dried Italian herbs, and minced garlic. Allow them to marinate while you prepare the mash.
After the potatoes are cooked, drain them and return them to the pot. Add milk, sour cream, butter, cheddar cheese, salt, and pepper. Mash until smooth and creamy, adjusting milk for desired consistency.
Heat a large skillet over medium-high heat. First, add the chicken breasts and cook for 5-7 minutes on each side until golden brown and cooked through. Remove and keep warm.
In the same skillet, cook the steak for about 4-5 minutes on each side for medium-rare, or longer to your desired doneness. Let it rest for a few minutes before slicing.
Plate the cheesy mash and top with the sliced steak and chicken breast. Sprinkle with grated Parmesan cheese and garnish with fresh parsley.