Place pepperoni on a hot grill, cut side down. Grill for 3 minutes per side. Remove from the grill and slice into 1/4-inch thick slices. In a large saute pan, heat the oil. When the oil is hot, add the onions and saute for 6 minutes. Add the mushrooms and saute until soft, about 5 minutes. Season with salt and pepper. Add the grilled pepperoni, garlic, basil and spinach. Saute for 3 minutes or until spinach has begun to wilt. Add the veal demi-glace and bring to a boil. Reduce heat to a simmer. Add the heavy cream and bring back up to a boil. Reduce heat and simmer for 5 minutes. Add the Parmesan cheese and mix well. Add the pasta and toss well. Season with salt and pepper.