Place potatoes in a pot with cold water and a hearty pinch of salt. Place over high heat and bring up to a boil. Cook potatoes until a knife can just pierce them but they’re not yet soft, about 5 minutes. Drain and dress potatoes with 1 tablespoon EVOO, salt and pepper.
Place a large, cast-iron skillet over medium heat with 1 turn of the pan EVOO, about 1 tablespoon. In a single layer, add chorizo, mushrooms (cap side down), garlic and potatoes, and cook until crispy and golden brown, 6-7 minutes. Deglaze pan with sherry, add parsley and toss to coat.