Grilled Steak and Potatoes with Mushrooms

Prick the potatoes with a fork and microwave on high until tender, 10 to 12 minutes. Wrap each potato in heavy-duty foil. Meanwhile, heat grill to medium-high. Place the mushrooms and garlic on a large piece of heavy-duty foil and sprinkle with 1/4 teaspoon each salt and pepper. Fold up the sides and add the wine, then seal the foil to form a pouch. Season the steak with 1/2 teaspoon each salt and pepper. Grill the steak to desired doneness, 5 to 7 minutes per side for medium-rare. Transfer to a cutting board and let rest for 5 minutes before slicing. While the steak is cooking, place the mushroom pouch and potatoes on the grill. Grill the potatoes until just tender, about 5 minutes. Grill the mushrooms, shaking the pouch occasionally, for 8 minutes. Transfer the mushrooms (and any juices) to a bowl and toss with the spinach, parsley, and sour cream. Serve the steak with the mushrooms and potatoes topped with sour cream, if desired.