Heat one tablespoon olive oil in a large sauté pan. Add the onion slices, and carefully turn with tongs to coat. As they warm, they’ll begin to collapse into the pan. Continue to cook, occasionally stirring, until browned, about twenty minutes.
Add the nutmeg, half of the salt and pepper, and the raisins, and toss to mix into the onions. Cool another five minutes. Pour in the wine, and cook at a rapid simmer until absorbed, about ten minutes. When the pan is fairly dry, add the spinach. Toss in with tongs. Once most of the spinach begins to wilt, remove to a bowl. The spinach will continue to wilt, so don’t wait until it’s completely wilted before removing to the bowl.
Using the same sauté pan, heat up the remaining tablespoon of oil over medium-high heat. Clean the cap and gills of the mushrooms using a brush or paper towel. I reserve a pastry brush for this, which does a great job of brushing dirt out of hidden nooks and crannies. If they feel dry, rub a little olive oil on their surfaces. But only a little. Mushrooms are very absorbent.
Place the mushrooms, cap side down, in the pan and cook for two – three minutes. Add the vegetable broth and thyme, and flip the mushrooms over. Cover the pan and cook for another two – three minutes. Flip again, and season the mushrooms with the remaining salt and pepper. Divide the onion – spinach mixture between the four mushrooms and top each with one tablespoon gorgonzola. Reduce the heat to medium, cover the pan, and cook for an additional two minutes.
Place the stuffed mushrooms on a serving plate and shower their beauty with pomegranate jewels.